drm/i915: Remove begin/finish_crtc_commit, v4.

drm/i915: Remove begin/finish_crtc_commit, v4.

This can all be done from the intel_update_crtc function. Split out the
pipe update into a separate function, just like is done for the planes.
Pull in all the changes done during fastset as well. It makes no sense
for it to still exist as a separate function.

Changes since v1:
- Inline intel_update_pipe_config()
Changes since v2:
- Add comments suggested by matt.
- Reorder commit_pipe_config() to remove all nesting. (Ville, Matt)
- Use intel_set_pipe_src_size((). (Matt)
Changes since v3:
- Move atomic_update_watermarks closer to the plane calls.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191004113514.17064-7-maarten.lankhorst@linux.intel.com
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
[mlankhorst: Replace 8 spaces with tabs in comment]