mtd: m25p80: Add support for Macronix MX25L25635E

This is a 256Mbit (32MiB) part so minor changes were made to support
4-byte addressing.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>