drivers/gpio: stm32: Fix gpio_stm32_configure

Behavior of function gpio_stm32_configure has been modified
during driver factorization. Various gpio settings (speed, mode, ..)
are applied conditionally while they used to be applied in sequence,
unconditionally before this change. As a consequence some
combinations of configurations are no more applied (like speed for
alternate mode). This of course has impact in some use cases.
Rework functions in order to apply settings unconditionally. Take
advantage of the change to reduce code size.

This change impacts all SoCs except F1 series.

Fixes #12544

Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>