build-image change the default target to the devkit

Signed-off-by: Angus Ainslie (Purism) <angus@akkea.ca>

build-image

@@ -103,7 +103,7 @@ cwd=$(pwd)
 
 distro=${DIST:-buster+ci}
 mirror=${MIRROR:-"http://deb.debian.org/debian"}
-pureos_board=imx6
+pureos_board=devkit
 build_type=current
 NULL=
 uboot_bin=