ARM: shmobile: Use names of power domains for adding devices to them

Make the power management code under arch/arm/mach-shmobile/ use
names of power domains instead of pointers to domain objects for
adding devices to the domains.  This will allow us to put the
domain objects into tables and register them all in one shot
going forward.

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