ARM: shmobile: sh7372: completely switch over to using pm-rmobile API

Now, all sh7372 platforms are switched over to use pm-rmobile base PM domain,
and no one is using original sh7372_pm_domain APIs.
We can remove these, switching has been fully completed.

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>