thermal-engine: Add virtual sensor for GPU and apply ss algorithm on
GPU throttling

1) GPU virtual sensor is based on the difference of  gpu0-usr and
   cpu0-silver-usr
2) Apply SS-algorithm to throttle GPU and have clock floor at 414MHz

Test: Running Manhattan 3.1 to check the throttling behavior
Bug: 113332262
Change-Id: I330d366de0de6e98b027c1111857432360d7b845
diff --git a/thermal-engine-blueline-novr-prod.conf b/thermal-engine-blueline-novr-prod.conf
index 1b3c7f6..9df79f8 100644
--- a/thermal-engine-blueline-novr-prod.conf
+++ b/thermal-engine-blueline-novr-prod.conf
@@ -28,6 +28,26 @@
 device_max_limit 1363200
 time_constant 0
 
+[HOT-SKIN-VIRTUAL]
+algo_type               virtual
+trip_sensor             fps-therm-adc
+sensors                 gpu0-usr cpu0-silver-usr
+list_cnt                2
+weights                 1 -1
+set_point               40000
+set_point_clr           37000
+sampling                1000
+math                    0
+
+[VIRTUAL-SS-GPU-SKIN]
+algo_type               ss
+sensor                  HOT-SKIN-VIRTUAL
+device                  gpu
+sampling                1000
+set_point               8000
+set_point_clr           2000
+device_max_limit        414000000
+
 [SKIN-MONITOR]
 algo_type		monitor
 sampling		1000