mtd: add helper functions library and header files for GPMI NAND driver

bch-regs.h : registers file for BCH module
gpmi-regs.h: registers file for GPMI module
gpmi-lib.c: helper functions library.

Signed-off-by: Huang Shijie <b32955@freescale.com>
Acked-by: Marek Vasut <marek.vasut@gmail.com>
Tested-by: Koen Beel <koen.beel@barco.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@intel.com>