mvebu: cortexa9: set DTS dir for 6.6

With 6.6, all DTSes were moved to their vendor subdirectories. ARM64
DTSes already used this scheme, but 32 bit Cortex A9 did not, prior
to 6.6. Introduce a kernel version check to keep backward compatibility
with 6.1.

Once we fully move to 6.6, we can set DTS_DIR for all mvebu subtargets
and move our downstream DTSes into the vendor subdirectory as well.

Suggested-by: Robert Marko <robimarko@gmail.com>
Signed-off-by: Stijn Segers <foss@volatilesystems.org>

target/linux/mvebu/image/cortexa9.mk

@@ -3,6 +3,10 @@
 # Copyright (C) 2012-2016 OpenWrt.org
 # Copyright (C) 2016 LEDE-project.org
 
+ifneq ($(KERNEL),6.1)
+DTS_DIR := $(DTS_DIR)/marvell
+endif
+
 define Build/fortigate-header
   ( \
     dd if=/dev/zero bs=384 count=1 2>/dev/null; \