powerpc: Export dcr_ind_lock to fix build error

Fix build error caused by missing export:

ERROR: "dcr_ind_lock" [drivers/net/ethernet/ibm/emac/ibm_emac.ko] undefined!

Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>