drm/i915: Handle joined pipes inside hsw_crtc_disable()

Reorganize the crtc disable path to only deal with the
master pipes/transcoders in intel_old_crtc_state_disables()
and offload the handling of joined pipes to hsw_crtc_disable().
This makes the whole thing much more sensible since we can
actually control the order in which we do the per-pipe vs.
per-transcoder modeset steps.

v2: Use the name 'pipe_crtc' for the per-pipe crtc pointer

Tested-by: Vidya Srinivas <vidya.srinivas@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240409163502.29633-4-ville.syrjala@linux.intel.com