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>

target/Config.in

@@ -32,6 +32,9 @@ config PCIE_SUPPORT
 config PCMCIA_SUPPORT
 	bool
 
+config PINCTRL_SUPPORT
+	bool
+
 config PWM_SUPPORT
 	bool