arm64: Add support for NanoPI NEO2

Add overlay files and activate devicetree file for NanoPi NEO2 featuring
Allwinner H5 ARM64 core.
To enable sound, dma and codec drivers are enabled for build.

Submitted by: Manuel Stühn (freebsdnewbie@freenet.de)
MFC after: 1 month
Differential Revision: https://reviews.freebsd.org/D20129