linux: add support for vendor dirs for appended DTBs

Take the basename of the appended DTBs to workaround the following problem:

(cd .../arch/arm/boot; for dtb in cirrus/ep93xx-edb9302
 do if test -e ${dtb}.dtb ; then dtbpath=${dtb}.dtb
 else dtbpath=dts/${dtb}.dtb ; fi
 cat zImage ${dtbpath} > zImage.${dtb} || exit 1; done)
/bin/sh: line 1: zImage.cirrus/ep93xx-edb9302: No such file or directory

Necessary to support ARM Linux starting from commit 724ba6751532
("ARM: dts: Move .dts files to vendor sub-directories"), i.e. Linux v6.4+.

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

linux/linux.mk

@@ -468,7 +468,7 @@ define LINUX_APPEND_DTB
 			else \
 				dtbpath=dts/$${dtb}.dtb ; \
 			fi ; \
-			cat zImage $${dtbpath} > zImage.$${dtb} || exit 1; \
+			cat zImage $${dtbpath} > zImage.$$(basename $${dtb}) || exit 1; \
 		done)
 endef
 ifeq ($(BR2_LINUX_KERNEL_APPENDED_UIMAGE),y)