mtd: add a helper to get the supported features for ONFI nand

add a helper to get the supported features for ONFI nand.
Also add the neccessary macros.

Signed-off-by: Huang Shijie <b32955@freescale.com>
Reviewed-and-tested-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>