drm/i915/mtl: Update OA mux whitelist for MTL

0x20cc (WAIT_FOR_RC6_EXIT on other platforms) is repurposed on MTL. Use
a separate mux table to verify oa configs passed by user.

Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221212220902.1819159-4-umesh.nerlige.ramappa@intel.com