drm/i915/perf: Skip the i915_perf_init for dg2

i915_perf is not enabled for dg2 yet, hence skip the feature
initialization.

Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
cc: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220215053115.6023-1-ramalingam.c@intel.com