omap3: Make SPL_OMAP3_ID_NAND depend on NAND_OMAP_GPMC

This specific bit logic is used to determine what NAND chip is present
on a board in order to then know what revision of the board we have and
so what DDR chips are present. We can only do this if we have a NAND
chip, and so we will have NAND_OMAP_GPMC enabled.

Signed-off-by: Tom Rini <trini@konsulko.com>