Added RG8 fragment output format

Tying up loose ends from the new output formats project.
One of the missing outputs was the RG8 format, which I added here.

Change-Id: I865ad4c462e892dbc3a7820003b2390b54453ee9
Reviewed-on: https://swiftshader-review.googlesource.com/7171
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
diff --git a/src/Shader/PixelProgram.cpp b/src/Shader/PixelProgram.cpp
index 0f7d0ed..a1c01c4 100644
--- a/src/Shader/PixelProgram.cpp
+++ b/src/Shader/PixelProgram.cpp
@@ -604,6 +604,7 @@
 			case FORMAT_A8B8G8R8:
 			case FORMAT_SRGB8_X8:
 			case FORMAT_SRGB8_A8:
+			case FORMAT_G8R8:
 			case FORMAT_R8:
 			case FORMAT_A8:
 			case FORMAT_G16R16:
@@ -741,6 +742,7 @@
 			case FORMAT_X8B8G8R8:
 			case FORMAT_SRGB8_X8:
 			case FORMAT_SRGB8_A8:
+			case FORMAT_G8R8:
 			case FORMAT_R8:
 			case FORMAT_A8:
 			case FORMAT_G16R16: