drm/radeon/dpm: resume fixes for some systems

Setting the power state prior to restoring the display
hardware leads to blank screens on some systems.  Drop
the power state set from dpm resume.  The power state
will get set as part of the mode set sequence.  Also
add an explicit power state set after mode set resume
to cover PX and headless systems.

bug:
https://bugzilla.kernel.org/show_bug.cgi?id=76761



Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>