drm/i915: Add hw.pipe_mode to allow bigjoiner pipe/transcoder split

With bigjoiner, there will be 2 pipes driving 2 halves of 1 transcoder,
because of this, we need a pipe_mode for various calculations, including
for example watermarks, plane clipping, etc.

v10:
* remove redundant pipe_mode assignment (Ville)
v9:
* pipe_mode in state dump nd state check (Ville)
v8:
* Add pipe_mode in readout in verify_crtc_state (Ville)
v7:
* Remove redundant comment (Ville)
* Just keep mode instead of pipe_mode (Ville)
v6:
* renaming in separate function, only pipe_mode here (Ville)
* Add description (Maarten)
v5:
* Rebase (Manasi)
v4:
* Manual rebase (Manasi)
v3:
* Change state to crtc_state, fix rebase err  (Manasi)
v2:
* Manual Rebase (Manasi)

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Animesh Manna <animesh.manna@intel.com>
[vsyrjala:
* Fix state checker
* Fix state dump
* Use pipe_mode for linetime watermarks
* Make sure pipe_mode normal timings are correct since the
  silly ddb code uses them
* Drop the redundant pipe_mode copies from intel_modeset_pipe_config()
  and intel_crtc_copy_uapi_to_hw_state()
* Use drm_mode_copy() all over]
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201112191718.16683-7-ville.syrjala@linux.intel.com