hwc: Enable downscale feature through system property

Add support to turn the MDP downscale feature ON through the
use of a system property. 'sys.hwc.mdp_downscale_enabled' shall be
set to 'true' in build.prop file to enable this functionality.

This is required for OEMs that might have privacy concerns over panel
size information being exposed.

Change-Id: I354b25b1fdabe5786aed7552f2afccda35412467
diff --git a/libhwcomposer/hwc_utils.cpp b/libhwcomposer/hwc_utils.cpp
index d2104ed..68461c7 100644
--- a/libhwcomposer/hwc_utils.cpp
+++ b/libhwcomposer/hwc_utils.cpp
@@ -238,6 +238,14 @@
     ctx->mBufferMirrorMode = false;
     ctx->mVPUClient = NULL;
 
+    // Read the system property to determine if downscale feature is enabled.
+    ctx->mMDPDownscaleEnabled = false;
+    char value[PROPERTY_VALUE_MAX];
+    if(property_get("sys.hwc.mdp_downscale_enabled", value, "false")
+            && !strcmp(value, "true")) {
+        ctx->mMDPDownscaleEnabled = true;
+    }
+
 #ifdef VPU_TARGET
     if(qdutils::MDPVersion::getInstance().is8092())
         ctx->mVPUClient = new VPUClient(ctx);