lib/mpi: export mpi_rshift

A subsequent patch will make the crypto/dh's dh_is_pubkey_valid() to
calculate a safe-prime groups Q parameter from P: Q = (P - 1) / 2. For
implementing this, mpi_rshift() will be needed. Export it so that it's
accessible from crypto/dh.

Signed-off-by: Nicolai Stange <[e-mail]>
Reviewed-by: Hannes Reinecke <[e-mail]>
Signed-off-by: Herbert Xu <[e-mail]>

lib/mpi/mpi-bit.c

···
 	}
 	MPN_NORMALIZE(x->d, x->nlimbs);
 }
+EXPORT_SYMBOL_GPL(mpi_rshift);
 
 /****************
  * Shift A by COUNT limbs to the left