automake: add SWR to `make distcheck' gallium drivers

Will allows us to catch missing files and build issues before getting
the tarball out for general consumption.

Cc: "12.0" <mesa-stable@lists.freedesktop.org>
Cc: Tim Rowley <timothy.o.rowley@intel.com>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
1 file changed