spi: zynqmp: gqspi: update chip select assert/de-assert timeout loop

This patch does following:

- Updates chip select assert/de-assert timeout loop using jiffies count

- Adds generic fifo entry in zynqmp_qspi_chipselect() function to
  assure the CS assert and CS de-assert

Signed-off-by: Ranjit Waghmode <ranjit.waghmode@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>