gpio: stm32: create include file for driver private data

The stm32 gpio driver private data are not needed in arch include files,
they are not used by code except for stm32 gpio and pincontrol drivers,
using the same IP; the defines for this IP is moved in a new file
"stm32_gpio_priv.h" in driver/gpio.

This patch avoids to have duplicated file gpio.h for each SOC
in MPU directory mach-stm32mp and in each MCU directory arch-stm32*
and allows to remove CONFIG_GPIO_EXTRA_HEADER for all STM32.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>