gpio: stm32f7: Add gpio bank holes management

In some STM32 SoC packages, GPIO bank has not always 16 gpios.
Several cases can occur, gpio hole can be located at the beginning,
middle or end of the gpio bank or a combination of these 3
configurations.

For that, gpio bindings offer the gpio-ranges DT property which
described the gpio bank mapping.

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