ARM: shmobile: R-Mobile: Generalize adding/looking up special PM domains

Make adding special PM domains to an array, and looking them up
later, more generic, so it can be used for all special hardware blocks.
The type of PM domain is also stored, so rmobile_setup_pm_domain() can
use a switch() statement instead of a chain of if/else statements.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>