gallium: add separate PIPE_CAP_INT64_DIVMOD

gallium: add separate PIPE_CAP_INT64_DIVMOD

Nouveau does not currently have logic to implement this as a library
function. Even though such a library could be written, there's no big
advantage to do it that way for now given that int64 is a very uncommon
use-case. Allow a driver to expose INT64 without supporting division and
modulo operations.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>