pinctrl: stm32: Update stm32_pinctrl_get_gpio_dev()

Due to gpio holes management, stm32_pinctrl_get_gpio_dev() must
be updated.

stm32_pinctrl_get_gpio_dev() returns from a given pin selectors
the corresponding bank gpio device and the gpio_offset inside this
gpio bank.

Update also all functions which makes usage of stm32_pinctrl_get_gpio_dev.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>