ARM: OMAP2+: nand: unify init functions

Helper function for updating nand platform data has been
added the capability to take timing structure arguement.
Usage of omap_nand_flash_init() has been replaced by modifed
one, omap_nand_flash_init was doing things similar to
board_nand_init except that NAND CS# were being acquired
based on bootloader setting. As CS# is hardwired for a given
board, acquiring gpmc CS# has been removed, and updated with
the value on board.

NAND CS# used in beagle board & omap3evm was found to be CS0.
Thomas Weber <thomas.weber.linux@googlemail.com> reported
that value of devkit8000 to be CS0. Overo board was found
to be using CS0 based on u-boot, while google grep says
omap3touchbook too has CS0.

Signed-off-by: Afzal Mohammed <afzal@ti.com>
Reviewed-by: Jon Hunter <jon-hunter@ti.com>
Acked-by: Igor Grinberg <grinberg@compulab.co.il>