drm/i915: Sanitize MBUS joining

drm/i915: Sanitize MBUS joining

If the system boots with MBUS joining enabled but we disable
the relevant pipe during sanitation we later get into trouble
as the rest of the code doesn't expect MBUS joining to be
enabled unless the set of active pipes is in agreement.

We could relax some of the MBUS joining related checks during
normal atomic commits to let this slide, but that might also
let some real bugs through. So let's sanitize the MBUS joining
instead. And in order to keep things more or less in sync we'll
do the related credit, cdclk/mdclk ratio, etc. updates as well.

We'll stick to sturct drm_i915_private for now (instead of
struct intel_display) since the rest of the skl wm code does the
same, and we might need to bakport this.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241031155646.15165-6-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>