spi: Remove SPI_OPM_RX_EXTN

spi: Remove SPI_OPM_RX_EXTN

SPI_OPM_RX_EXTN is a combination of all rx opmode's
and spi driver shall use any one of the rx mode at
a time not the combination and it is true in case of
flash where spi_flash_table mention combination of
supported read opmodes so-that the required one
will pick based on the rx mode from spi driver.

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