treewide: use only board_name function to get name

Do not parse /tmp/sysinfo/board_name, /proc/cpuinfo or the device tree
compatible string directly. Always use the board_name function to get
the board name.

The admswconfig package still reads /proc/cpuinfo directly. The code
looks somehow broken and the whole adm5120 which uses this package
looks unmaintained. Leave it as it is for now.

Signed-off-by: Mathias Kresin <dev@kresin.me>

target/linux/ipq806x/base-files/lib/upgrade/zyxel.sh

@@ -68,7 +68,7 @@ zyxel_do_flash() {
 
 zyxel_do_upgrade() {
 	local tar_file="$1"
-	local board=$(cat /tmp/sysinfo/board_name)
+	local board=$(board_name)
 	local rootfs="$(zyxel_get_rootfs)"
 	local kernel=