Introduce driver for Freescale Felix switch

It is found on boards equipped with LS1028A SoC.
802.1q VLAN grouping is supported.
An external MDIO device is used for communicating with PHYs.
The driver is built as a module by default, it is not included
in GENERIC kernel config.

Submitted by: Lukasz Hajec <lha@semihalf.com>

Kornel Duleba <mindal@semihalf.com>

Obtained from: Semihalf
Sponsored by: Alstom Group
Differential Revision: https://reviews.freebsd.org/D30923