u-boot-sinovoip-bpi-m3: Update to u-boot-master

Update to u-boot-master model, moved MAINTAINER to uboot@. This brings the
version from 2016.05 (super old) to 2017.09 under the unified FreeBSD u-boot
model.

All of the patches previously here have been made redundant, either by
upstream or by using our U-Boot repository with FreeBSD patches applied.

Reviewed by: imp, manu
Approved by: imp, jmcneill (maintainer)
Differential Revision: https://reviews.freebsd.org/D13352