Update to u-boot-master model, moved MAINTAINER to imp@ for consistency
with other u-boot-master ports that I sampled. This brings the version from
2016.05 (super old) to 2017.09 under the unified FreeBSD u-boot model.
There are some AXP patches that might need to be upstreamed; I'll review those
and double-check that they're still needed, but they at least have no effect on
current -HEAD. IIRC, dc1sw regulator is supplier for emac PHY.