radeon: With DRI1, if we have HW stencil, only expose fbconfigs with stencil.

radeon: With DRI1, if we have HW stencil, only expose fbconfigs with stencil.

Otherwise simple apps like glxgears pick up a DirectColor visual since the X
server mixes the depth 32 visual in with the other GLX visuals, and this seems
to result in a (mostly) black screen due to a bad ColorMap for a lot of people.

The bad ColorMap may be a bug in the apps, the X server or X driver, and
regardless of that I think the X server should ideally make the depth 32 GLX
visual separate from the rest again, but in the meantime this makes us cope.

(depth_bits is either 16 or 24, never 0)