drm/i915: Don't bypass LRC on CHV

drm/i915: Don't bypass LRC on CHV

The docs are unclear as usual, so it's not clear whether LRC should be
bypassed, performed normally or GRC code should be used as the LRC code.
Some old docs stated that LRC bypass ought to be used, more recent ones
no longer say that. Some docs indicated that we could use GRC as the LRC
code on CHV, but the BIOS doesn't do that, so let's not do it either.

Besides to enable LRC bypass properly, I believe we should set the bit
already before deasserting cmnreset.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Deepak S<deepak.s@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>