drivers/gpio: stm32f1: AFIO init should happen before GPIO inits

GPIO initialization was moved to PRE_KERNEL_1 with commit
590162a5cc06c72b70dee93f410b878bc0935f1f.
This had the consequence of having AFIO init done after GPIO init
as a consequence, this sequence ends up with AFIO clock disabled,
and hence negative impact on AFIO expected services.

Additionally, to save some flash, compile out afio init when not
required.

Fixes #38870

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