mfd: Add missing #ifdef around tc3589x PM block

The CONFIG_PM code was unconditionally compiled in despite
the dev_pm_ops only being included into the driver struct
if used. Fix this by adding the missing #ifdef.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>