drm/i915: Allow bigjoiner for MST

We need bigjoiner support with MST functionality
for MST monitor resolutions > 5K to work.
Adding support for the same.

v2: Addressed review comments from Jani.
Revert rejection of MST bigjoiner modes and add
functionality

v3: Fixed pipe_mismatch WARN for mst_master_transcoder
Credits-to: Manasi Navare <navaremanasi@chromium.org>

v4: Utilize intel_crtc_joined_pipe_mask() also for handling
    bigjoiner slave pipes for MST case(Stan)
[v5: vsyrjala: chunked the modeset squence stuff out,
               removed bogus mst master transcoder hack,
	       keep mgr_lock near the full_pbn check]
[v6: vsyrjala: Calculate DSC slices correctly for bigjoiner (Imre)]

Reviewed-by: Manasi Navare <navaremanasi@chromium.org>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Signed-off-by: Vidya Srinivas <vidya.srinivas@intel.com>
Co-developed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240409163502.29633-7-ville.syrjala@linux.intel.com