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>

arch/alpha/math-emu/math.c

@@ -401,3 +401,5 @@ alpha_fp_emul_imprecise (struct pt_regs *regs, unsigned long write_mask)
 egress:
 	return si_code;
 }
+
+EXPORT_SYMBOL(__udiv_qrnnd);