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/lib/preinit/07_set_iface_mac

@@ -1,47 +0,0 @@
-#!/bin/sh
-# Copyright (C) 2018 OpenWrt.org
-
-RECOVERY_PART=/dev/mmcblk0p1
-
-preinit_set_mac_address() {
-	local mac
-
-	. /lib/functions.sh
-	. /lib/functions/system.sh
-
-	case $(board_name) in
-	"unielec,u7623"*)
-		if [ -b $RECOVERY_PART ]; then
-			insmod nls_cp437
-			insmod nls_iso8859-1
-			insmod fat
-			insmod vfat
-			mkdir -p /tmp/recovery
-			mount -o rw,noatime $RECOVERY_PART /tmp/recovery
-
-			if [ -f "/tmp/recovery/mac_addr" ];
-			then
-				mac=$(cat /tmp/recovery/mac_addr)
-			else
-				mac=$(cat /sys/class/net/eth0/address)
-				echo "$mac" > /tmp/recovery/mac_addr
-			fi
-
-			sync
-			umount /tmp/recovery
-			rm -rf /tmp/recovery
-		fi
-
-		ip link set dev wan address $mac 2> /dev/null
-
-		mac=$(macaddr_add $mac 1)
-
-		ip link set dev lan0 address $mac 2>/dev/null
-		ip link set dev lan1 address $mac 2>/dev/null
-		ip link set dev lan2 address $mac 2>/dev/null
-		ip link set dev lan3 address $mac 2>/dev/null
-		;;
-	esac
-}
-
-boot_hook_add preinit_main preinit_set_mac_address

target/linux/mediatek/base-files/lib/preinit/79_move_config

@@ -1,21 +0,0 @@
-#!/bin/sh
-# Copyright (C) 2015 OpenWrt.org
-
-. /lib/upgrade/common.sh
-
-RECOVERY_PART=/dev/mmcblk0p1
-
-move_config() {
-	if [ -b $RECOVERY_PART ]; then
-		insmod nls_cp437
-		insmod nls_iso8859-1
-		insmod fat
-		insmod vfat
-		mkdir -p /recovery
-		mount -o rw,noatime $RECOVERY_PART /recovery
-		[ -f "/recovery/$BACKUP_FILE" ] && mv -f "/recovery/$BACKUP_FILE" /
-		umount /recovery
-	fi
-}
-
-boot_hook_add preinit_mount_root move_config