mtd: FSMC NAND use the PrimeCell identifier macros

The FSMC actually has a standard ARM PrimeCell ID register, and
the "revision" part of that register contains the thing that
the code is looking at. Reuse the infrastructure from the AMBA
bus abstraction and rid local defines.

Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>