drivers: soc: xilinx: Add ZynqMP power domain driver

The zynqmp-genpd driver communicates the usage requirements
for logical power domains / devices to the platform FW.
FW is responsible for choosing appropriate power states,
taking Linux' usage information into account.

Signed-off-by: Rajan Vaja <rajan.vaja@xilinx.com>
Signed-off-by: Jolly Shah <jolly.shah@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>