As GLES2 doesn't support LogiOps, we have to fallback
here. GLES2 programing guide's statement is as below:
"In addition, LogicOp is removed as it is very
infrequently used by applications and the OpenGL ES
working group did not get requests from independent
software vendors (ISVs) to support this feature in
OpenGL ES 2.0."
So, I think, fallback here may not a big deal ;).
Signed-off-by: Zhigang Gong <zhigang.gong@linux.intel.com>