drm/i915/selftests: Add delay to stabilize frequency in live_rps_power

Add delays to allow frequency stabilization before power measurement
to fix sporadic power conservation issues in live_rps_power test.

v2:
  - Move delay to respective function (Badal)

Signed-off-by: Sk Anirban <sk.anirban@intel.com>
Reviewed-by: Badal Nilawar <badal.nilawar@intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241203061114.2790448-1-sk.anirban@intel.com

Author: sanirban-999

drivers/gpu/drm/i915/gt/selftest_rps.c

@@ -1125,6 +1125,7 @@ static u64 measure_power(struct intel_rps *rps, int *freq)
 static u64 measure_power_at(struct intel_rps *rps, int *freq)
 {
 	*freq = rps_set_check(rps, *freq);
+	msleep(100);
 	return measure_power(rps, freq);
 }