ARM: shmobile: Move r8a7740's PM domain objects to a table

Instead of giving a name to every r8a7740's PM domain object, put
them all into a table and use rmobile_init_domains(), introduced by a
previous patch, for initializing them all altogether.  Also, use
pm_genpd_add_subdomain_names() for adding A3SP as a subdomain of A4S.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Magnus Damm <damm@opensource.se>