kirkwood: use the generic board detect

Drop the target specific detection function in favour of the generic
one provided by base-files.

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

target/linux/kirkwood/base-files/lib/upgrade/platform.sh

@@ -11,8 +11,8 @@ platform_do_upgrade() {
 	local board="$(board_name)"
 
 	case "$board" in
-	"linksys-audi"|\
-	"linksys-viper")
+	"linksys,audi"|\
+	"linksys,viper")
 		platform_do_upgrade_linksys "$ARGV"
 		;;
 	*)