ARM: shmobile: sh7372: add pm-rmobile domain support

This patch adds pm-rmobile common API base PM domain.
sh7372 CPU/platform will switch to using it from
original implementation

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>