ipq40xx: add support for FRITZ!Box 7520

This model, also know as "1&1 HomeServer", shares the same features as 7530.

The vendor firmware has artificial software limitations: only 2 of the 4
LAN-Ports are GBit, and the USB-Host is only v2.0.

With OpenWrt, USB is already working at v3.0.

Signed-off-by: Andre Heider <a.heider@gmail.com>
(updated commit message to reflect current state)
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>

target/linux/ipq40xx/image/generic.mk

@@ -269,6 +269,8 @@ define Device/avm_fritzbox-7530
 	$(call Device/FitImageLzma)
 	DEVICE_VENDOR := AVM
 	DEVICE_MODEL := FRITZ!Box 7530
+	DEVICE_ALT0_VENDOR := AVM
+	DEVICE_ALT0_MODEL := FRITZ!Box 7520
 	SOC := qcom-ipq4019
 	DEVICE_PACKAGES := fritz-caldata fritz-tffs-nand
 endef