mtd: nand: omap: remove redundant platform specific header: arch-xx/omap_gpmc.h

mtd: nand: omap: remove redundant platform specific header: arch-xx/omap_gpmc.h

Currently there are two sets of omap_gpmc.h header files
(a) arch/arm/include/asm/omap_gpmc.h
 common header file for all platforms, containing defines and declarations used
 by GPMC NAND driver.

(b) arch/arm/include/asm/arch-xx/omap_gpmc.h
 SoC platform specific header file containing defines like ECC layout.

This patch removes platform specific arch-xx/omap_gpmc.c because:
 - GPMC hardware engine is common for all SoC platforms hence only (a) is enough
 - ECC layout is now defined in omap_nand.c driver itself based on ecc-scheme
   selected. Hence all ECC layout declarations in (b) are redundant.

Build tested using: ./MAKEALL -s am33xx -s omap3 -s omap4 -s omap5

Signed-off-by: Pekon Gupta <pekon@ti.com>