x86: switch to 5.4 kernel

Seems to be working fine on apu2 and QEMU, it's 99.9% upstream stuff
anyway. Lets start wider userbase testing.

Signed-off-by: Petr Štetiar <ynezz@true.cz>

target/linux/x86/Makefile

@@ -13,7 +13,7 @@ FEATURES:=squashfs ext4 vdi vmdk pcmcia targz fpu
 SUBTARGETS:=generic legacy geode 64
 MAINTAINER:=Felix Fietkau <nbd@nbd.name>
 
-KERNEL_PATCHVER:=4.19
+KERNEL_PATCHVER:=5.4
 KERNEL_TESTING_PATCHVER:=5.4
 
 KERNELNAME:=bzImage