xen/arm: zynqmp: introduce zynqmp specific defines

xen/arm: zynqmp: introduce zynqmp specific defines

Introduce zynqmp specific defines for the firmware calls.
See EEMI:
https://www.xilinx.com/support/documentation/user_guides/ug1200-eemi-api.pdf

The error codes are described, under XIlPM Error Codes:
https://www.xilinx.com/support/documentation/user_guides/ug1137-zynq-ultrascale-mpsoc-swdev.pdf

- pm_api_id
These are the EEMI function IDs. Unavoidable.

- pm_ret_status
These are the EEMI return statuses. Unavoidable.

Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Signed-off-by: Stefano Stabellini <stefanos@xilinx.com>