Enabled pixel unpack buffers

Setting pixel unpack buffers was already supported, but they were still
unused. This cl enables them to be used as data when loading a texture.

This fixes ~200 pbo related dEQP tests.

Change-Id: Ibada594185dab4f14bebf892e4df817a7dfe8401
Reviewed-on: https://swiftshader-review.googlesource.com/5640
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>

src/OpenGL/libGLESv2/Context.h

diff --git a/src/OpenGL/libGLESv2/Context.h b/src/OpenGL/libGLESv2/Context.h
index 10e6a5a..918807a 100644
--- a/src/OpenGL/libGLESv2/Context.h
+++ b/src/OpenGL/libGLESv2/Context.h
@@ -634,6 +634,7 @@
 	Buffer *getPixelPackBuffer() const;
 	Buffer *getPixelUnpackBuffer() const;
 	Buffer *getGenericUniformBuffer() const;
+	const GLvoid* getPixels(const GLvoid* data) const;
 	bool getBuffer(GLenum target, es2::Buffer **buffer) const;
 	Program *getCurrentProgram() const;
 	Texture2D *getTexture2D() const;