drm/xe/guc: Eliminate RPa frequency caching

drm/xe/guc: Eliminate RPa frequency caching

Remove the cached pc->rpa_freq field and refactor RPA frequency handling
to fetch values directly from hardware registers on each request.

v2: Check graphics version instead of platform (Rodrigo)
v3: Fix graphics version check (Badal)

Suggested-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Suggested-by: Badal Nilawar <badal.nilawar@intel.com>
Signed-off-by: Sk Anirban <sk.anirban@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patch.msgid.link/20251112185153.3593145-6-sk.anirban@intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>