pinctrl: abx500: fix abx500_gpio_dbg_show_one() to show pull up/down

- rework abx500_gpio_dbg_show_one() to take in account pull up/down
  feature available on AB8540 only.
- add abx500_get_pull_updown() needed by abx500_gpio_dbg_show_one()
- rename abx500_config_pull_updown() to abx500_set_pull_updown()

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