configure.ac: add option --with-gallium-drivers=DIRS

This removes all the --enable-gallium-$driver options and --disable-gallium.

Gallium can be disabled by --with-gallium-drivers= (without parameters).

Default is:
--with-gallium-drivers=r300,swrast

Reviewed-by: Alex Deucher <alexdeucher@gmail.com>
1 file changed