mtd: spi-nor: Add the SNOR_F_4B_OPCODES flag

Some flash_info entries have the SPI_NOR_4B_OPCODES flag set to let the
core know that the flash supports 4B opcode. While this solution works
fine for id-based caps detection, it doesn't work that well when relying
on SFDP-based caps detection. Let's add an SNOR_F_4B_OPCODES flag so
that the SFDP parsing code can set it when appropriate.

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>