Backport UBI patches from 4.2.0-rc5

UBIFS over UBI is the default filesystem used in QCOM chipsets
that use NAND storage.

Recently a number of stability and performance fixes were
added to the kernel that address issues ranging from data loss
to bootup issues. The fastmap feature has also undergone a rewrite
to help address issues of stability and memory leaks.

Backport and bring in all the changes to ensure stability and
better performance for the NAND based devices.

* The patches included are:
  UBI: Remove unnecessary `\'
  UBI: Use static class and attribute groups
  UBI: add a helper function for updatting on-flash layout volumes
  UBI: Fastmap: Do not add vol if it already exists
  UBI: Init vol->reserved_pebs by assignment
  UBI: Fastmap: Rename variables to make them meaningful
  UBI: Fastmap: Remove unnecessary `\'
  UBI: Fastmap: Use max() to get the larger value
  UBI: block: Dynamically allocate minor numbers
  UBI: block: Add missing cache flushes
  UBI: power cut emulation for testing
  UBI: Fastmap: Fall back to scanning mode after ECC error
  UBI: Fastmap: Remove is_fm_block()
  UBI: Fastmap: Add blank line after declarations
  UBI: Fastmap: Remove else after return.
  UBI: Fastmap: Introduce may_reserve_for_fm()
  UBI: Fastmap: Introduce ubi_fastmap_init()
  UBI: Fastmap: Wire up WL accessor functions
  UBI: Add accessor functions for WL data structures
  UBI: Move fastmap specific functions out of wl.c
  UBI: Fastmap: Add new module parameter fm_debug
  UBI: Fastmap: Make self_check_eba() depend on fastmap self checking
  UBI: Fastmap: Add self check to detect absent PEBs
  UBI: Fix stale pointers in ubi->lookuptbl
  UBI: Fastmap: Enhance fastmap checking
  UBI: Add initial support for fastmap self checks
  UBI: Fastmap: Rework fastmap error paths
  UBI: Fastmap: Prepare for variable sized fastmaps
  UBI: Fastmap: Locking updates
  UBI: Fastmap: Set used_ebs only for static volumes
  UBI: Fastmap: Fix race after ubi_wl_get_peb()
  UBI: Fastmap: Fix leb_count unbalance
  UBI: Fastmap: Make WL pool size 50% of user pool size
  UBI: Fastmap: Switch to ro mode if invalidate_fastmap() fails
  UBI: Fastmap: Remove eba_orphans logic
  UBI: Fastmap: Remove bogus ubi_assert()
  UBI: Fastmap: Fix race in ubi_eba_atomic_leb_change()
  UBI: Remove alloc_ai() slab name from parameter list
  UBI: Fastmap: Fix memory leak while attaching
  UBI: Fastmap: Fix fastmap usage in ubi_volume_notify()
  UBI: Fastmap: Wrap fastmap specific function in a ifdef
  UBI: Fastmap: Notify user in case of an ubi_update_fastmap() failure
  UBI: Fastmap: Fix memory leaks while closing the WL sub-system
  UBI: Fastmap: Don't allocate new ubi_wl_entry objects
  UBI: Fastmap: Make ubi_refill_pools() fair
  UBI: Split __wl_get_peb()
  UBI: Fastmap: Fix races in ubi_wl_get_peb()
  UBI: Fastmap: Ensure that all fastmap work is done upon WL shutdown
  UBI: Fastmap: Ensure that only one fastmap work is scheduled
  UBI: align comment for readability
  UBI: fix missing brace control flow
  UBI: block: Fix checking for NULL instead of IS_ERR()
  UBI: block: Continue creating ubiblocks after an initialization error
  UBI: Block: Explain usage of blk_rq_map_sg()
  UBI: fix soft lockup in ubi_check_volume()
  UBI: Fastmap: Care about the protection queue
  UBI: do propagate positive error codes up
  UBI: clean-up printing helpers
  UBI: extend UBI layer debug/messaging capabilities - cosmetics
  UBI: Block: Add blk-mq support
  UBI: Add initial support for scatter gather
  UBI: rename_volumes: Use UBI_METAONLY
  UBI: Implement UBI_METAONLY
  UBI: vtbl: Use ubi_eba_atomic_leb_change()
  UBI: Extend UBI layer debug/messaging capabilities
  Revert "mtd: ubi: reduce messages during scrub all PEBs"
  Revert "UBI: Fastmap: Fix memory leak while attaching"

Change-Id: I1e967405f29127295d2ebc3a546eedad05de931c
Signed-off-by: Nikhilesh Reddy <reddyn@codeaurora.org>