base-files: board_detect: allow specifying the generated file

Allow passing a filename to change the location of the generated
board.json.

Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>

package/base-files/files/bin/board_detect

 #!/bin/sh
 
-[ -d "/etc/board.d/" -a ! -f "/etc/board.json" ] && {
+CFG=$1
+
+[ -n "$CFG" ] || CFG=/etc/board.json
+
+[ -d "/etc/board.d/" -a ! -f "$CFG" ] && {
 	for a in `ls /etc/board.d/*`; do
 		[ -x $a ] || continue;
 		$(. $a)
 	done
 }
 
-[ -f "/etc/board.json" ] || return 1
+[ -f "$CFG" ] || return 1

package/base-files/files/lib/functions/uci-defaults.sh

 #!/bin/ash
 
-CFG=/etc/board.json
-
 . /lib/functions.sh
 . /usr/share/libubox/jshn.sh