hammerhead: enable MDP composition

Change-Id: I1075c98dccc176f10697fafbe6c6ba87f400cede
diff --git a/device.mk b/device.mk
index 9812034..5fff121 100644
--- a/device.mk
+++ b/device.mk
@@ -108,6 +108,9 @@
     ro.sf.lcd_density=320
 
 PRODUCT_PROPERTY_OVERRIDES += \
+    persist.hwc.mdpcomp.enable=true
+
+PRODUCT_PROPERTY_OVERRIDES += \
     ro.hwui.texture_cache_size=72 \
     ro.hwui.layer_cache_size=48 \
     ro.hwui.r_buffer_cache_size=8 \