drm/radeon/dpm: fix a typo in the rv6xx mclk setup

Need to set high for the last two entries.  Looks
like a copy and paste typo.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
drm/radeon/dpm: fix displaygap programming on rv6xx

Need to use the driver state rather than the register
state since the displays may not be enabled when the
power state is programmed.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
drm/radeon/dpm: implement force performance levels for rv6xx

Allows you to limit the selected power levels via sysfs.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
drm/radeon/dpm: fix r600_enable_sclk_control()

Actually program the correct register to enable
engine clock scaling control.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>