drm/i915/mtl: PERF_LIMIT_REASONS changes for MTL

PERF_LIMIT_REASONS register for MTL media gt is different now.

v2: Avoid static inline for intel_gt_perf_limit_reasons_reg() (Jani)

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Badal Nilawar <badal.nilawar@intel.com>
Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220910143844.1755324-3-ashutosh.dixit@intel.com