Include e6000sw driver in ARMADA38X configuration

e6000sw Marvell switch driver was added to files
and Armada38x kernel configuration file.

Submitted by: Bartosz Szczepanek <bsz@semihalf.com>
Obtained from: Semihalf
Sponsored by: Stormshield
Differential revision: https://reviews.freebsd.org/D8178