drivers: mtd: spi: Allow Quad I/O enablement for ISSI SPI flash devices alongside spi-nor-tiny.c subsystem

Hi All,

I noticed this was missing from the spi-nor-tiny.c subsystem while trying to use an ISSI SPI flash device with the U-Boot SPL.

This patch will allow Quad (4x) I/O mode to be enabled with ISSI flash devices while inside the U-Boot SPL / using spi-nor-tiny.c.

Sincerely, Nathan