spi: zynq_qspi: Remove the flash command table in driver

Remove the flash command table from driver as it no longer
need to check for the command and write to TXD based on that.

Signed-off-by: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>