ARM: shmobile: r8a7790 SYSC setup code

Add r8a7790 SYSC power management support.

Signed-off-by: Hisashi Nakamura <hisashi.nakamura.ak@renesas.com>
Signed-off-by: Ryo Kataoka <ryo.kataoka.wt@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>