uterm: drm3d: fix GL_UNPACK_ROW_LENGTH(_EXT) macro

Khronos "fixed" their new OpenGLES2 headers and added a bunch of _EXT
suffixes. Now we need to test for both, the old and new macros, yay!

Thanks to Yichao Yu for spotting that.

Reported-by: Yichao Yu <yyc1992@gmail.com>
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>