ath79: Upstream b53 DSA driver for Ubiquiti EdgeSwitch 8XP

ath79: Upstream b53 DSA driver for Ubiquiti EdgeSwitch 8XP

The swconfig-based b53 driver for the BCM53128 switch stopped working
after commits b2cfed48f6 (Revert "swconfig: fix Broadcom b53 support")
and e4e410733f (kernel: export switch_generic_set_link() symbol). This
rendered the 8 LAN ports of the EdgeSwitch 8XP non-functional, so the
image compilation for the device was disabled (5a1d7d8c1b).

This commit adds the kmod-dsa-b53-mdio and kmod-dsa-b53 packages
with the upstream B53 DSA driver, replacing the swconfig-based
kmod and kmod-switch-bcm53xx-mdio downstream ones that are not used by
any other device.

The 8 LAN ports of the EdgeSwitch 8XP are usable again. The 02_network
init script has been updated with the new DSA interfaces lan1 .. lan8.

Image building has been reenabled for the device, adding the usual DSA
incompatibility notice.

Tested on a Ubiquiti EdgeSwitch 8XP.

Signed-off-by: Roger Pueyo Centelles <roger.pueyo@guifi.net>
Link: https://github.com/openwrt/openwrt/pull/11680
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>