egl: define missing EGL_KHR_create_context enums
egl: define missing EGL_KHR_create_context enums

This makes sure the EGL_KHR_create_context enums are always defined in
cogl-winsys-egl.c so we will build with drivers that don't support this
extension. Cogl will do runtime checks to explicitly check that the
extension is available before ever referencing these enums so this is
safe to do.

https://bugzilla.gnome.org/show_bug.cgi?id=694537

Reviewed-by: Neil Roberts <822ec91a7ef82248fd36162ca8ac3283eba70848@linux.intel.com>

gcampax/cogl,djdeath/cogl-android,djdeath/cogl-android,gcampax/cogl,djdeath/cogl-android,djdeath/cogl,djdeath/cogl,gcampax/cogl,djdeath/cogl,gcampax/cogl