ath79: mikrotik: compile SWCONFIG and AR8216_PHY as modules

ath79: mikrotik: compile SWCONFIG and AR8216_PHY as modules

Unset the SWCONFIG symbol and AR8216_PHY which selects SWCONFIG. Add
kmod-switch-ar8xxx, which enables AR8216_PHY, to DEFAULT_PACKAGES for the
subtarget. With this, swconfig driver will be now compiled as a module, as
kmod-switch-ar8xxx selects kmod-swconfig.

Refresh the config-default file for ath79/mikrotik while at it.

This change makes it possible to disable the swconfig driver for MikroTik
RouterBOARD 960PGS (hEX PoE/PowerBox Pro).

Signed-off-by: Chester A. Unal <chester.a.unal@arinc9.com>