add overlay folder to Makefile

The autopatcher thingy seems borked as it seems this line should be included automatically (??)

Author: EvilOlaf

patch/kernel/archive/sunxi-6.18/patches.armbian/arm-dts-overlay-Add-Overlays-for-sunxi.patch

@@ -4852,6 +4852,18 @@ index 000000000000..111111111111
 +        uart7_pi_pins = "/fragment@1/__overlay__:pinctrl-0:0";
 +    };
 +};
+diff --git a/arch/arm/boot/dts/allwinner/Makefile b/arch/arm/boot/dts/allwinner/Makefile
+index f71392a55df8..36fb1355c415 100644
+--- a/arch/arm/boot/dts/allwinner/Makefile
++++ b/arch/arm/boot/dts/allwinner/Makefile
+@@ -279,5 +279,7 @@ dtb-$(CONFIG_MACH_SUN9I) += \
+ 	sun9i-a80-cubieboard4.dtb
+ dtb-$(CONFIG_MACH_SUNIV) += \
+ 	suniv-f1c100s-licheepi-nano.dtb \
+ 	suniv-f1c200s-lctech-pi.dtb \
+ 	suniv-f1c200s-popstick-v1.1.dtb
++
++subdir-y       := $(dts-dirs) overlay
 -- 
 Armbian