garnet: Defer refresh rate changes when screen is off

Some devices with video mode panels experience refresh rate mismatches when the screen is turned off. Specifically:
- The scheduler sets the refresh rate to 120 Hz after the screen turns off at 60 Hz (VRR idle).
- However, the HWC ignores this change, resulting in SurfaceFlinger (SF) incorrectly assuming the device is at 120 Hz when the display is turned back on.
- This causes a mismatch, as HWC continues rendering at 60 Hz, leading to inconsistencies.

To enable this behavior, set the following property:
- `debug.sf.defer_refresh_rate_when_off=1`

Change-Id: I46fd9e6b983138c1f625d52a65451eb04ce42820

props/vendor.prop

@@ -136,6 +136,7 @@ debug.sf.predict_hwc_composition_strategy=0
 debug.sf.set_idle_timer_ms=1100
 debug.sf.treat_170m_as_sRGB=1
 debug.sf.use_phase_offsets_as_durations=1
+debug.sf.defer_refresh_rate_when_off=1
 persist.sys.sf.color_mode=0
 persist.sys.sf.color_saturation=1.0
 ro.hardware.egl=adreno