geom was removed in e968975 ("gallium: remove the geom_flags param
from is_format_supported", Tue Mar 8 00:01:58 2011 +0100), but the
documentation of it was left over. Let's bring the documentation up
to date.
Signed-off-by: Erik Faye-Lund <kusmabite@gmail.com> Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>