spi: cadence_qspi: Add quad write support

Use quad write if SPI_TX_QUAD flag is set.

Tested quad write on Stratix 10 SoC board (Micron
serial NOR flash, mt25qu02g)

Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>
3 files changed