uboot-imx

arm64: zynqmp: Added support of mmio read and write commands

This patch added support of mmio read and write commands. These commands
can be used to read and write registers from the u-boot command line.
It can be useful in debugging.

Signed-off-by: Vipul Kumar <vipul.kumar@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>