sm6250-common: Explicitly disable "Enable GL comp backpressure"

When blur is enabled,
There is severe lag in; Launcher3 while scrolling apps in App drawer, Scrolling through recents and occasionally on QS pull down.

Enabling or completely removing the prop here d6233e0e7c doesn't seem to make an effect.
Explicitly disabling the "Enable GL comp backpressure" prop seems to slove the issue.

Lag & janks are gone now, even with blur.

Change-Id: Ia82d84d6ee867caa52ae93b72fbff132070bf808
Signed-off-by: helliscloser <mrumais@gmail.com>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>

vendor.prop

@@ -178,6 +178,7 @@ ro.incremental.enable=true
 persist.sys.sf.color_mode=9
 debug.sf.disable_client_composition_cache=0
 debug.sf.enable_adpf_cpu_hint=true
+debug.sf.enable_gl_backpressure=0
 persist.sys.sf.color_saturation=1.0
 persist.sys.sf.native_mode=2
 ro.hardware.egl=adreno