drm/i915/display/icl: Enable master-slaves in trans port sync

As per the display enable sequence, we need to follow the enable sequence
for slaves first with DP_TP_CTL set to Idle and configure the transcoder
port sync register to select the corersponding master, then follow the
enable sequence for master leaving DP_TP_CTL to idle.
At this point the transcoder port sync mode is configured and enabled
and the Vblanks of both ports are synchronized so then set DP_TP_CTL
for the slave and master to Normal and do post crtc enable updates.

v11:
* Rebase (Manasi)
v10:
* in trans sync mode, dont stop link train for tgl (Manasi)
v9:
Remove update_scanline_offset to rebase on Maarten's patch (Manasi)
v8:
* Rebase on Maarten's patches (Manasi)
v7:
* Use ffs(slaves) to get slave crtc (Ville)
v6:
* Modeset implies active_changed, remove one condition (Maarten)
v5:
* Fix checkpatch warning (Manasi)
v4:
* Reuse skl_commit_modeset_enables() hook (Maarten)
* Obtain slave crtc and states from master (Maarten)
v3:
* Rebase on drm-tip (Manasi)
v2:
* Create a icl_update_crtcs hook (Maarten, Danvet)
* This sequence only for CRTCs in trans port sync mode (Maarten)

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191018172725.1338-4-manasi.d.navare@intel.com