ARM: shmobile: r8a7790 CA7-SCU enablement

Power on CA7 SCU in case of booting from a CA15 core.

Signed-off-by: Gaku Inami <gaku.inami.xw@bp.renesas.com>
[damm@opensource.se: Converted to use broken out SYSC code]
Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>