meson.build: report graphics backends separately

meson.build: report graphics backends separately

To enable accelerated VirtIO GPUs for the guest we need the rendering
support on the host, which currently it's reported in the configuration
summary under the "dependencies" section. Add a graphics backend section
and report the status of the VirGL and Rutabaga support libraries.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20231222114846.2850741-1-alex.bennee@linaro.org>
[Remove from dependencies as suggested by Philippe. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>