dts: remove README from Makefile

See: #6681

Author: sanderhollaar

arch/arm/boot/dts/overlays/Makefile

@@ -1,6 +1,6 @@
 # Overlays for the Raspberry Pi platform
 
-dtb-$(CONFIG_ARCH_BCM2835) += overlay_map.dtb hat_map.dtb README
+dtb-$(CONFIG_ARCH_BCM2835) += overlay_map.dtb hat_map.dtb
 
 dtbo-$(CONFIG_ARCH_BCM2835) += \
 	act-led.dtbo \