mvebu: add Linux 5.15 as testing kernel

Run-tested on the cortexa9 subtarget (Turris Omnia).

Signed-off-by: Rui Salvaterra <[email protected]>

target/linux/mvebu/Makefile

@@ -10,6 +10,7 @@ FEATURES:=fpu usb pci pcie gpio nand squashfs ramdisk boot-part rootfs-part lega
 SUBTARGETS:=cortexa9 cortexa53 cortexa72
 
 KERNEL_PATCHVER:=5.10
+KERNEL_TESTING_PATCHVER:=5.15
 
 include $(INCLUDE_DIR)/target.mk