tools: build squashfs (v3) for ath79

tools: build squashfs (v3) for ath79

Certain Netgear and AVM devices use BE squashfs for the kernel image. As
squashfs4 only supports creating LE images, add squashfs (v3) into
the tools to be built for ath79.

Trying to use an LE squashfs (thus trying to use squashfs4 only for
building the image) for the kernel image results in the bootloader
barfing and stopping.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Zoltan HERPAI <wigyori@uid0.hu>