drm/i915/display: Share code between intel_drrs_flush and intel_drrs_invalidate

Both functions are pretty much equal, with minor changes that can be
handled by a single parameter.

v3:
- not scheduling work from invalidate operations

Cc: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210903221036.34770-2-jose.souza@intel.com