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 <daniel@makrotopia.org>

include/target.mk

@@ -315,6 +315,9 @@ ifeq ($(DUMP),1)
     ifneq ($(CONFIG_PCIEPORTBUS),)
       FEATURES += pcie
     endif
+    ifneq ($(CONFIG_PINCTRL),)
+      FEATURES += pinctrl
+    endif
     ifneq ($(CONFIG_PWM),)
       FEATURES += pwm
     endif