alpha: __udiv_qrnnd should be exported

When building an alpha kernel with mpi set as module, I hit this build
error:
ERROR: "__udiv_qrnnd" [lib/mpi/mpi.ko] undefined!
make[2]: *** [scripts/Makefile.modpost:92: __modpost] Error 1
make[1]: *** [Makefile:1266: modules] Error 2

This is due to __udiv_qrnnd not exported.
Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Matt Turner <mattst88@gmail.com>