parisc/power: Move soft-power into power.c

parisc/power: Move soft-power into power.c

Move the soft-power ctl table into parisc/power.c. As a consequence the
pwrsw_enabled var is made static.

This is part of a greater effort to move ctl tables into their
respective subsystems which will reduce the merge conflicts in
kernel/sysctl.c.

Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Joel Granados <joel.granados@kernel.org>