firmware: xilinx: Add pm api function for PL config reg readback

Adds PM API for performing Programmable Logic(PL) configuration
register readback. It provides an interface to the firmware(pmufw)
to readback the FPGA configuration register.

Signed-off-by: Nava kishore Manne <nava.kishore.manne@amd.com>
Acked-by: Xu Yilun <yilun.xu@intel.com>
Link: https://lore.kernel.org/r/20230224120738.329416-2-nava.kishore.manne@amd.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>