drm/i915/perf: Store a pointer to oa_format in oa_buffer

DG2 introduces OA reports with 64 bit report header fields. Perf OA
would need more information about the OA format in order to process such
reports. Store all OA format info in oa_buffer instead of just the size
and format-id.

v2: Drop format_size variable (Ashutosh)

Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@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/20221026222102.5526-11-umesh.nerlige.ramappa@intel.com