This adds a driver/gl/cogl-texture-gl.c file and moves some gl specific
bits from cogl-texture.c into it. The moved symbols were also given a
_gl_ infix and the calling code was updated accordingly.
Reviewed-by: Neil Roberts <neil@linux.intel.com>
(cherry picked from commit 2c9e81de70cc02d72b1ce9013c49e39300a05b6a)
