firmware: xilinx: Implement ZynqMP power management APIs

Add Xilinx ZynqMP firmware APIs to set suspend mode
and inform firmware that master has initialized its
own power management.

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>