ipq4018: add initial IPQ4018/IPQ4019 support

This is for the Qualcomm Atheros quad-core ARMv7 SoC with built-in
2x2 2GHz and 5GHz ath10k devices.

It's enough (with an upcoming set of config files) to netboot
on an ASUS router I have here and get to a single core mountroot
prompt.