mtd: nand_base: Only use GET/SET FEATURES command on chips that support them.

Spansion's S34MLx chips support ONFI but not the GET/SET FEATURES calls.

Signed-off-by: David Mosberger <dmosberger@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>