spi: cadence-quadspi: Enable SPI_TX_QUAD

commit 7a78c89eb58bad042c55b7b0234300ab9f561919 from
git://git.ti.com/ti-linux-kernel/ti-linux-kernel.git



Enable SPI_TX_QUAD in spi_controller->mode_bits to add support for
the 1S-4S-4S operations.

Signed-off-by: Santhosh Kumar K <s-k6@ti.com>
Tested-by: Prasanth Babu Mantena <p-mantena@ti.com>
Signed-off-by: Xulin Sun <xulin.sun@windriver.com>