spi: Use mode for rx mode flags

spi: Use mode for rx mode flags

Make rx mode flags as generic to spi, earlier mode_rx is
maintained separately because of some flash specific code.

Cc: Simon Glass <sjg@chromium.org>
Cc: Bin Meng <bmeng.cn@gmail.com>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
Cc: Vignesh R <vigneshr@ti.com>
Cc: Mugunthan V N <mugunthanvnm@ti.com>
Signed-off-by: Jagan Teki <jteki@openedev.com>