drm/i915: Skip wm/ddb readout for disabled pipes

commit 0211c2a0 upstream.

The stuff programmed into the wm/ddb registers of planes
on disabled pipes doesn't matter. So during readout just
leave our software state tracking for those zeroed.

This should avoid us trying too hard to clean up after
whatever mess the VBIOS/GOP left in there. The actual
hardware state will get cleaned up if/when we enable
the pipe anyway.

Cc: stable@vger.kernel.org
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/5711


Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220617195948.24007-1-ville.syrjala@linux.intel.com


Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
(cherry picked from commit b183db8f)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>