ARM: shmobile: soc-core: add R-mobile PM domain common APIs

This patch adds Renesas R-mobile series common PM domain APIs.
R-mobile CPU can use/switch this API

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Acked-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>