mtd: add helpers to set/get features for ONFI nand

Add the set-features(0xef)/get-features(0xee) helpers for ONFI nand.
Also add the necessary macros.

Signed-off-by: Huang Shijie <b32955@freescale.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>