Adding functionality to stencils

Two minor features are required for the blitFramebuffer
implementation in OpenGL ES 3:
- lockStencil with x,y coordinates
- getting the stencil format (new getStencilFormat function)

Change-Id: I83ccccefe70dbbedd05b5d82bc75d30f689c4abe
Reviewed-on: https://swiftshader-review.googlesource.com/7490
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>

src/OpenGL/libGLES_CM/Device.cpp

diff --git a/src/OpenGL/libGLES_CM/Device.cpp b/src/OpenGL/libGLES_CM/Device.cpp
index 6587d36..b66c323 100644
--- a/src/OpenGL/libGLES_CM/Device.cpp
+++ b/src/OpenGL/libGLES_CM/Device.cpp
@@ -455,8 +455,8 @@
 
 			if(source->hasStencil())
 			{
-				sw::byte *sourceBuffer = (sw::byte*)source->lockStencil(0, PUBLIC);
-				sw::byte *destBuffer = (sw::byte*)dest->lockStencil(0, PUBLIC);
+				sw::byte *sourceBuffer = (sw::byte*)source->lockStencil(0, 0, 0, PUBLIC);
+				sw::byte *destBuffer = (sw::byte*)dest->lockStencil(0, 0, 0, PUBLIC);
 
 				unsigned int width = source->getWidth();
 				unsigned int height = source->getHeight();