targets: add PINCTRL_SUPPORT auto-feature

targets: add PINCTRL_SUPPORT auto-feature

Not all targets have CONFIG_PINCTRL=y set in their kernel config.
Let's introduce a feature for that so kernel module packages which
select or depend on CONFIG_PINCTRL=y may depend on that, so we can
try to prevent leaking CONFIG_PINCTRL=y also into targets which do
not require it.

Signed-off-by: Daniel Golle <[email protected]>