sparc32,leon: add notify_cpu_starting()

Otherwise cpu_active_mask will not set, which lead to other issue.

Signed-off-by: Yong Zhang <yong.zhang0@gmail.com>
Signed-off-by: Konrad Eisele <konrad@gaisler.com>
Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>