glx: Fix build in GLX_DIRECT_RENDERING !GLX_USE_APPLEGL !GLX_USE_DRM case

glx: Fix build in GLX_DIRECT_RENDERING !GLX_USE_APPLEGL !GLX_USE_DRM case

Some untangling to fix building in the dri_platform=none, --enable-driglx-direct
case, where only driswast can be used.

Turn the test for including the glXGetScreenDriver()/glXGetScreenDriver()
interface used by xdriinfo from !GLX_USE_APPLEGL into a positive form, as it is
only useful when dri_platform=drm

Add additional GLX_USE_DRM tests so DRI[123] renderers are only used when
dri_platform=drm

Note that swrast and indirect must still be disabled in the APPLEGL case at the
moment, which makes things more complex than they need to be.  More untangling
is needed to allow that

Signed-off-by: Jon TURNEY <jon.turney@dronecode.org.uk>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>