mxs: enable 5.15 as testing kernel

Signed-off-by: Zoltan HERPAI <[email protected]>

target/linux/mxs/Makefile

@@ -11,6 +11,7 @@ FEATURES:=ext4 rtc usb gpio
 CPU_TYPE:=arm926ej-s
 
 KERNEL_PATCHVER:=5.10
+KERNEL_TESTING_PATCHVER:=5.15
 
 KERNELNAME:=zImage dtbs