regulator: fixed: Modify enable-active-high behavior

Regulator should not be enabled at probe time if regulator-boot-on
property is not in the dt node.

"enable-active-high" property is only used to indicate the GPIO
polarity.

See kernel documentation :
 - Documentation/devicetree/bindings/regulator/fixed-regulator.yaml
 - Documentation/devicetree/bindings/regulator/gpio-regulator.yaml

Signed-off-by: Christophe Kerello <christophe.kerello@st.com>
Signed-off-by: Patrice Chotard <patrice.chotard@st.com>