drm/radeon: Add ability to get and change dpm state when radeon PX card is turned off

This fixing commit 4f2f2039

bug:
https://bugzilla.kernel.org/show_bug.cgi?id=76321



Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org