Add kernel config and dts files for an aml8726-m3

Add kernel config and dts files for an aml8726-m3
based device.
Following u-boot commands allow FreeBSD boot on
Yiyate Android TV Box (aml8726-m3):

tv open 480p
mmc rescan 0
fatload mmc 0 0x80100000 kernel.bin
go 0x80100000

The current FreeBSD driver doesn't program the video
clocks so the u-boot tv command is necessary in order
for the frame buffer to be useful (otherwise it can
be skipped).

The SD card for the Yiyate Android TV Box doesn't need
anything special beyond creating a FAT16 and a UFS
filesystem.

Differential Revision:	https://reviews.freebsd.org/D2636
Submitted by:	John Wehle