pinctrl: zynqmp: Add pinctrl driver

Add pinctrl driver for Xilinx ZynqMP SOC. This driver is compatible with
linux device tree parameters for configuring pinmux and pinconf.

Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/2d7eefa83c8c0129f7243a25de56a289e948f6c6.1645626183.git.michal.simek@xilinx.com