drm/i915/perf: Add Wa_1508761755:dg2

Disable Clock gating in EU when gathering the events so that EU events
are not lost.

v2: Fix checkpatch issues
v3: User MCR helpers to write to MC reg
v4: Indent correctly (checkpatch)

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/20221026222102.5526-12-umesh.nerlige.ramappa@intel.com