Disable EGL (and thus EGLFS) if we're not using OpenGL ES

Disable EGL (and thus EGLFS) if we're not using OpenGL ES

EGL support in src/platformsupport/eglconvenience requires OpenGL ES
to be enabled, so it makes no sense to test for the presence of EGL if
we're not enabling OpenGL ES.

EGLFS has similar requirements, so ensure it gets disabled
too. Otherwise we're going to get lots of undefined symbols in the
EGLFS plugin to things in QtPlatformSupport that did not get compiled
in either.

Change-Id: Ie55dd2e2597ec0594aa589ee8aac150c71104b46
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>