mtd: m25p80: add support of octal mode I/O transfer

Add support for octal mode I/O data transfer based on the controller (spi)
mode.
Assign hw-capability mask bits for octal transfer.

Signed-off-by: Yogesh Narayan Gaur <yogeshnarayan.gaur@nxp.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Boris Brezillon <bbrezillon@kernel.org>