mediatek: split base-files into subtargets

This splits some base-files across subtargets, as done previously
on ath79 and ramips and also introduced for mt7629 subtarget here
already. Most of the existing base-files content is specific to
mt7623.

While at it, apply the following fixes:
- Remove lots of trailing whitespaces
- Remove wildcard on unielec,u7623-02-emmc-512m
- Remove inconsistent quotation marks in cases

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Acked-by: John Crispin <john@phrozen.org>

target/linux/mediatek/base-files/etc/board.d/02_network

@@ -1,41 +0,0 @@
-#!/bin/sh
-
-. /lib/functions.sh
-. /lib/functions/uci-defaults.sh
-. /lib/functions/system.sh
-
-mediatek_setup_interfaces()
-{
-	local board="$1"
-
-	case $board in
-	'mediatek,mt7623a-rfb-emmc')
-		ucidef_set_interface_lan "lan0 lan1 lan2 lan3"
-		ucidef_set_interface_wan eth1
-		;;
-	'bananapi,bpi-r2'|\
-	"unielec,u7623"*)
-		ucidef_set_interfaces_lan_wan "lan0 lan1 lan2 lan3" "wan"
-		;;
-	esac
-}
-
-mediatek_setup_macs()
-{
-	local board="$1"
-
-	case $board in
-	"unielec,u7623"*)
-		mac=$(cat /sys/class/net/wan/address)
-		ucidef_set_interface_macaddr "wan" $mac
-		;;
-	esac
-}
-
-board_config_update
-board=$(board_name)
-mediatek_setup_interfaces $board
-mediatek_setup_macs $board
-board_config_flush
-
-exit 0