ARM: shmobile: Remove shmobile_smp_scu_boot_secondary()

Remove shmobile_smp_scu_boot_secondary() since
it is no longer used. CPU boot vector setup is
instead handled by CPU notifiers.

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