Add r8a7791 SYSC power management support.
Signed-off-by: NKeita Kobayashi <keita.kobayashi.ym@renesas.com>
Acked-by: NMagnus Damm <damm+renesas@opensource.se>
[horms+renesas@verge.net.au: rebased]
Signed-off-by: NSimon Horman <horms+renesas@verge.net.au>