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/rb532/base-files/lib/upgrade/platform.sh

@@ -15,10 +15,8 @@ platform_pre_upgrade() {
 }
 
 platform_nand_pre_upgrade() {
-	local board_name="$(cat /tmp/sysinfo/board_name)"
-
 	mtd erase kernel
-	tar xf "$1" sysupgrade-$board_name/kernel -O | nandwrite -o /dev/mtd0 -
+	tar xf "$1" "sysupgrade-$(board_name)/kernel" -O | nandwrite -o /dev/mtd0 -
 }
 
 platform_do_upgrade() {