drm/i915/vrr: Add helper for parsing value to be written into TRANS_PUSH

drm/i915/vrr: Add helper for parsing value to be written into TRANS_PUSH

On Lunarlake and onwards it is possible to generate PSR "frame change"
event using TRANS_PUSH mechanism. As a preparation add new helper to parse
value to be written into TRANS_PUSH register. Setting
LNL_TRANS_PUSH_PSR_PR_EN is done in upcoming change.

Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Link: https://patch.msgid.link/20260127124120.1069026-4-jouni.hogander@intel.com