ARM: shmobile: Add SCU boot function using argument

Add a shmoible_boot_scu function that assumes that the base address
of the SCU is passed in r0. This code is free from inline virtual
to physical address conversion.

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