mtd: nand: omap: remove unused #defines from common omap_gpmc.h

OMAP NAND driver can detect Page-size and OOB-size of NAND device from ONFI
params or nand_id[] table. And based on that it defines ECC layout.
This patch
1) removes following board configs used for defining NAND ECC layout
	- GPMC_NAND_ECC_LP_x16_LAYOUT (for large page x16 NAND)
	- GPMC_NAND_ECC_LP_x8_LAYOUT  (for large page x8 NAND)
	- GPMC_NAND_ECC_SP_x16_LAYOUT (for small page x16 NAND)
	- GPMC_NAND_ECC_SP_x8_LAYOUT  (for small page x8 NAND)

2) removes unused #defines in common omap_gpmc.h depending on above configs

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

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