tests/functional/test_aarch64_virt_gpu: Skip if "dbus" display isn't available

tests/functional/test_aarch64_virt_gpu: Skip if "dbus" display isn't available

This test currently fails if the "dbus" display has not been compiled
into the binary (which can happen when CFI has been enabled, for example).
Check for the error message to skip the test in that case.

While we're at it, also make sure that this test is covered in the
right section in the MAINTAINERS file.

Message-ID: <20250325061609.272847-1-thuth@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>