soc: gd32: Drop PINCTRL from Kconfig.defconfig

This Kconfig has wrongly been added to defconfig files. It is not the
right place for it. It has never been the right place for it. Drivers
that need it should select the symbol in their Kconfig entries. Drop
PINCTL from Kconfig.defconfig and add proper select at Kconfig.gd32.

Fixes #78619

Signed-off-by: Gerson Fernando Budke <nandojve@gmail.com>