arm64: versal: Define zynqmp_mmio_write() for versal

arm64: versal: Define zynqmp_mmio_write() for versal

GQSPI driver is using it but this function is never called for Versal
because it is removed by linker. But function should be declared to avoid
this build warning:
drivers/spi/zynqmp_gqspi.c: In function 'zynqmp_qspi_set_tapdelay':
drivers/spi/zynqmp_gqspi.c:378:3: warning: implicit declaration of function
'zynqmp_mmio_write' [-Wimplicit-function-declaration]
  378 |   zynqmp_mmio_write(IOU_TAPDLY_BYPASS_OFST,

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma@amd.com>
Link: https://lore.kernel.org/r/20220825125906.11581-3-ashok.reddy.soma@amd.com
Signed-off-by: Michal Simek <michal.simek@amd.com>