ARM: shmobile: Let sh73a0 rely on SCU CPU notifier

Now when CPU notifiers are used for SCU boot vector
setup shmobile_smp_scu_boot_secondary() is no longer
needed.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>