mtd: m25p80: Add support for CAT25xxx serial EEPROMs

CAT25 chips (as manufactured by On Semiconductor, previously Catalyst
Semiconductor) are similar to the original M25Px0 chips, except:

- Address width can vary (1-2 bytes, in contrast to 3 bytes in M25P
  chips). So, implement convenient m25p_addr2cmd() and m25p_cmdsz()
  calls, and place address width information into flash_info struct;

- Page size can vary, therefore we shouldn't hardcode it, so get rid
  of FLASH_PAGESIZE definition, and place the page size information
  into flash_info struct;

- CAT25 EEPROMs don't need to be erased, so add NO_ERASE flag, and
  propagate it to the mtd subsystem.

[dwmw2: Fix up for conflicts with DMA safety patch]
Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>