Mark EGL_KHR_create_context as supported in the DisplayGLs.

BUG=angleproject:1149

Change-Id: I20671535680eb2c3b9c08205cee243b3aa5c5821
Reviewed-on: https://chromium-review.googlesource.com/297080Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>