drm/i915: Factor out a helper to check/compute all the CRTC states

Factor out intel_atomic_check_config() to check and compute all the CRTC
states. This will be used by a follow up patch to recompute/check the
state until required by BW limitations between CRTCs.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230921195159.2646027-9-imre.deak@intel.com