drm/i915: remove PSR BDW single frame update.

Single frame update is a feature available on BDW for PSR that allows
Source to send Sink only one frame and get it updated. Usually useful
when page flipping. However with our frontbuffer tracking where we force
psr exit on flips we don't need this feature.

Also after it got added here many workaround was added to documentation
to mask some bits when using single frame update. So the safest thing
is to just stop using it.

v2: Rebase after removing skip aux one and fixing typo on commit message.

Reviewed-by: Durgadoss R <durgadoss.r@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>