xilinx: zynqmp: Rename pm_api members to use generic name

Use generic name for pm_api structure member, so that pm_api
structure can be used other Xilinx platforms.

Structure definition will be moved to common file in upcoming
patch.

Signed-off-by: Tejas Patel <tejas.patel@xilinx.com>
Reviewed-by: Siva Durga Prasad Paladugu <siva.durga.paladugu@xilinx.com>
Signed-off-by: Jolly Shah <jollys@xilinx.com>