Use F16 render target when wide color rendering is enabled

Support F16 render targets in Skia pipeline. Enable readback from
F16 surface.

Test: device boots with Skia pipeline
Change-Id: Ib31e618be1a987de3736987a496c799693923594
diff --git a/libs/hwui/pipeline/skia/SkiaOpenGLPipeline.cpp b/libs/hwui/pipeline/skia/SkiaOpenGLPipeline.cpp
index 925db30..bf77446 100644
--- a/libs/hwui/pipeline/skia/SkiaOpenGLPipeline.cpp
+++ b/libs/hwui/pipeline/skia/SkiaOpenGLPipeline.cpp
@@ -73,9 +73,11 @@
     // setup surface for fbo0
     GrGLFramebufferInfo fboInfo;
     fboInfo.fFBOID = 0;
+    GrPixelConfig pixelConfig =
+            wideColorGamut ? kRGBA_half_GrPixelConfig : kRGBA_8888_GrPixelConfig;
 
     GrBackendRenderTarget backendRT(frame.width(), frame.height(), 0, STENCIL_BUFFER_SIZE,
-            kRGBA_8888_GrPixelConfig, fboInfo);
+            pixelConfig, fboInfo);
 
     SkSurfaceProps props(0, kUnknown_SkPixelGeometry);