Currently omap nand driver uses a field in platform data - phys_base
for passing the address space allocated by gpmc for nand. Use struct
resource instead. With this change omap nand driver has to get
address space from memory resource.

This helps in smooth migration of gpmc to driver.
Signed-off-by: NAfzal Mohammed <afzal@ti.com>
Signed-off-by: NTony Lindgren <tony@atomide.com>