accel/amdxdna: Poll MPNPU_PWAITMODE after requesting firmware suspend

accel/amdxdna: Poll MPNPU_PWAITMODE after requesting firmware suspend

After issuing a firmware suspend request, the driver must ensure that the
suspend operation has completed before proceeding. Add polling of the
MPNPU_PWAITMODE register to confirm that the firmware has fully entered
the suspended state. This prevents race conditions where subsequent
operations assume the firmware is idle before it has actually completed
its suspend sequence.

Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Reviewed-by: Maciej Falkowski <maciej.falkowski@linux.intel.com>
Signed-off-by: Lizhi Hou <lizhi.hou@amd.com>
Link: https://patch.msgid.link/20251202165427.507414-1-lizhi.hou@amd.com