drm/i915: Utilize intel_crtc_joined_pipe_mask() more

Unify the master vs. slave handling in
intel_ddi_post_disable_hdmi_or_sst() by looping over all the
pipes in one go.

This also lets us move the intel_crtc_vblank_off() calls to
happen in a consistent place vs. the transcoder disable.
Previously we did the master vs. slaves on different sides
of that.

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/20240409163502.29633-3-ville.syrjala@linux.intel.com