drm/i915: Use pipes instead crtc indices in PLL state tracking

drm/i915: Use pipes instead crtc indices in PLL state tracking

All the other places we have use pipes instead of crtc indices
when tracking resource usage. Life is easier when we do it
the same way always, so switch the dpll mgr to using pipes as
well. Looks like it was actually mixing these up in some cases
so it would not even have worked correctly except when the
device has a contiguous set of pipes starting from pipe A.
Granted, that is the typical case but supposedly it may not
always hold on modern hw.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210224144214.24803-4-ville.syrjala@linux.intel.com
Reviewed-by: Mika Kahola <mika.kahola@intel.com>