Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

firmware(9) is a subsystem to load binary data into the kernel via a
specially crafted module. There are several handrolled sollutions to this
problem in the tree already which will be replaced with this. They include
iwi(4), ipw(4), ispfw(4) and digi(4).

No objection from: arch
MFC after: 2 weeks
X-MFC after: some drivers have been converted