[POWERPC] Add missing native dcr dcr_ind_lock spinlock

The include/asm-powerpc/dcr-native.h declares extern spinlock_t dcr_ind_lock;
but it's actually isn't defined. This patch adds a missing dcr_ind_lock.

Signed-off-by: Valentine Barshak <vbarshak@ru.mvista.com>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>