drm/i915: Write watermarks for disabled pipes on gmch platforms

drm/i915: Write watermarks for disabled pipes on gmch platforms

We've excluded gmch platforms from writing the final watermarks
for any disabled pipe. IIRC the reason was perhaps some lingering
issue with the watermark merging across the pipes. But I can't
really see any reason for this anymore, so let's unify this behaviour.
The main benefit being more consistency in register dumps when
we don't have stale watermarks hanging around in the registers.
Functionally there should be no difference as the hardware just
ignore all of it when the pipe is disabled.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220622155452.32587-9-ville.syrjala@linux.intel.com
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>