drm/i915: Nuke 'realloc_pipes'

The 'realloc_pipes' bitmask is pointless. It is either:
a) the set of pipes which are already part of the state,
   in which case adding them again is entirely redundant
b) the set of all pipes which we then add to the state

Also the fact that 'realloc_pipes' uses the crtc indexes is
going to bite is at some point so best get rid of it quick.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191011200949.7839-3-ville.syrjala@linux.intel.com


Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>