libgpiod: depend on kernel version

Required kernel interface was introduced in kernel v4.8,
so add the kernel version as dependency for this library.

Signed-off-by: Michael Heimpold <mhei@heimpold.de>

libs/libgpiod/Makefile

@@ -34,7 +34,7 @@ define Package/libgpiod
   CATEGORY:=Libraries
   URL:=https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git
   TITLE:=Library for interacting with Linux's GPIO character device
-  DEPENDS:=@GPIO_SUPPORT
+  DEPENDS:=@GPIO_SUPPORT @(LINUX_4_9||LINUX_4_14)
 endef
 
 define Package/libgpiod/description