ARM: OMAP: voltage: voltage layer present, even when CONFIG_PM=n

Even when CONFIG_PM=n, we try to scale the boot voltage to a sane,
known value using OPP table to find matching voltage based on boot
frequency.  This should be done, even when CONFIG_PM=n to avoid
mis-configured bootloaders and/or boot voltage assumptions made by
boot loaders.

Also fixes various compile problems due to depenencies between voltage
domain and powerdomain code (also present when CONFIG_PM=n).

Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kevin Hilman <khilman@ti.com>