Add power domain control support for the r8a7779 SoC V2.

This adds support for 4 power domains for I/O Devices
together with code that can be used for CPU cores as well.

The only out of the ordinary experience is the need for
ioremap() of SYSC registers. Because of that we need to
execute some init function before setting up the domains.
Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>