mfd: intel_soc_pmic_chtwc: Turn Kconfig option into a bool

The PMIC provides ACPI OpRegions which must be available for other
drivers' PS0 / PS3 methods early-on as such it must be builtin as the
Kconfig help text already states.

Somehow its Kconfig option ended up being a tristate though, this fixes
this.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>