drm/i915: Split intel_update_crtc() into two parts

drm/i915: Split intel_update_crtc() into two parts

Split intel_update_crtc() into two parts such that the first
part performs all the non-vblank evasion preparatory stuff,
and the second part just does the vblank evasion stuff.

For now we just call these back to back so that there is
no funcitonal change.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230907122541.32261-3-ville.syrjala@linux.intel.com
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>