egl: Configs w/o double buffering support have no `EGL_WINDOW_BIT`.

egl: Configs w/o double buffering support have no `EGL_WINDOW_BIT`.

When users pass a config to `eglCreateWindowSurface` it requests double
buffering, but if the config doesn't have the appropriate `__DRIconfig`,
`eglCreateWindowSurface` fails with a `EGL_BAD_MATCH`.

Given that such behaviour is completely unacceptable, we drop the
`EGL_WINDOW_BIT` if we don't have at least one `__DRIconfig` supporting double
buffering, otherwise dropping the `EGL_PIXMAP_BIT`.

Fixes: 049f343e8ac "egl: Allow 24-bit visuals for 32-bit RGBA8888 configs"
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=67676
Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Hal Gentz <zegentzy@protonmail.com>