mtd: sh_flctl: Add support for error IRQ

When the data transfer between the controller and the NAND chip fails,
we now get notified.

Signed-off-by: Bastian Hecht <hechtb@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>