ipq806x: switch to 5.4 kernel

ipq806x has been tested for a lot and lots of people reported good results.
Switch the main kernel to 5.4 following the other targets.

Tested-by: Stefan Lippers-Hollmann <s.l-h@gmx.de> [ipq8065, NBG6817]
Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>

target/linux/ipq806x/Makefile

@@ -10,8 +10,7 @@ CPU_TYPE:=cortex-a15
 CPU_SUBTYPE:=neon-vfpv4
 SUBTARGETS:=generic
 
-KERNEL_PATCHVER:=4.19
-KERNEL_TESTING_PATCHVER:=5.4
+KERNEL_PATCHVER:=5.4
 
 KERNELNAME:=zImage Image dtbs