mtd: spi-nor: Add support for Macronix mx25u6435f serial flash

Add Macronix (mx25u6435f) 8MB flash to the list of supported chips.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>