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

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

The chip specific functions have been split out in their own
C files to simplify adding of new PHY chips.
Include the split out .c files in the module build too.

This is a driver for the physical layer chips used in ATM interfaces.
It currently supports the PMC Sierra Lite, Ultra and 622 chips and
the IDT 77105. The driver handles media options and state in a consistent
manner for ATM drivers. The next commit to the midway driver will make
it use utopia.