msm: kgsl: allow consistent CPU and GPU mappings

KGSL_GPUMEM_ALLOC_ID now takes a flag,
KGSL_MEMFLAGS_USE_CPU_MAP. When set, the GPU
mapping will be set up to match the CPU mapping
during mmap().  This feature is only supported when
using per process pagetables with the IOMMU. The
flags field of KGSL_GPUMEM_ALLOC_ID is copied back
to userspace and KGSL_MEMFLAGS_USE_CPU_MAP will
be cleared when this feature is not supported.

The IOMMU virtual address space has been adjusted
when perprocess pagetables is enabled so that the
entire userpace address range (0 to TASK_SIZE) can
have equivalent mappings on the IOMMU. For buffers
that do not have equivalent mappings, the address
range from PAGE_OFFSET to KGSL_IOMMU_GLOBAL_MEM_BASE
is used.

Change-Id: Ib61c03aa7453c3dd901c41e8fd297f66d402ae1a
Signed-off-by: Jeremy Gebben <jgebben@codeaurora.org>