cogl-framebuffer.c: GL_DEPTH_STENCIL not supported in gles
cogl-framebuffer.c: GL_DEPTH_STENCIL not supported in gles

There is GL_INVALID_ENUM error for GL_DEPTH_STENCIL when call
glRenderbufferStorage() with OpenGL ES backend. So enable this
only for OpenGL backend.

Signed-off-by: Robert Bragg <12e9293ec6b30c7fa8a0926af42807e929c1684f@linux.intel.com>

djdeath/cogl-android,collects/cogl,gcampax/cogl,gcampax/cogl,spatulasnout/cogl,Distrotech/cogl,djdeath/cogl,Distrotech/cogl,djdeath/cogl-android,djdeath/cogl,djdeath/cogl,Distrotech/cogl,spatulasnout/cogl,gcampax/cogl,collects/cogl,Distrotech/cogl,djdeath/cogl-android,gcampax/cogl