spi: zynqmp: gqspi: replace readl/writel by wrappers

This patch replaces all readl() and writel() calls by
zynqmp_gqspi_read() and zynqmp_gqspi_write() wrappers respectively.

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