drm/i915: Extract PIPE_CONF_CHECK_RECT()

Deduplicate the drm_rect comparisons.

We also drop the redundant pch_pfit.enabled check since the
pch_pfit.dst rectanble will be zeroed anyway when the pfit
is not enabled.

v2: Document why we drop the enabled check (Jani)

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220503182242.18797-7-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>