pinctrl: abx500: allow to set pull up

On ABx500 chip family, all pins support only pull down except for
AB8540 which supports pull up/down on some pins.
Rework abx500_pin_config_set to be able to set pull up on
pins which support this feature.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>