ipq4018: add initial IPQ4018/IPQ4019 support

Summary:
This adds required IPQ4018/IPQ4019 SoC support to boot.
It also includes support for disabling the ARMv7 hardware
breakpoint / debug stuff at compile time as this is
required for the IPQ SoCs, and printing out the undefined
instruction itself.

Test Plan: * compiled/booted on an IPQ4019 SoC AP

Reviewers: Core Team!

Subscribers: imp, andrew

Differential Revision: https://reviews.freebsd.org/D32538