u-boot-digi: Generalize boot script

Generalize the boot script used to boot Linux so that it can be shared
by multiple ConnectCore 6UL SOM based boards.

Signed-off-by: Alex Gonzalez <alex.gonzalez@digi.com>

recipes-bsp/u-boot/u-boot-digi/ccimx6ul/bootscript.txt

@@ -2,6 +2,6 @@
 # U-Boot bootscript for NAND images created by Yocto.
 #
 
-setenv fdt_file imx6ul-ccimx6ulsbcexpress.dtb
-setenv zimage zImage-ccimx6ulsbcexpress.bin
+setenv fdt_file imx6ul-${platform}.dtb
+setenv zimage zImage-${platform}.bin
 dboot linux nand ${mtdbootpart}

recipes-bsp/u-boot/u-boot-digi_2017.03.bb

@@ -30,6 +30,7 @@ UBOOT_ENV = "boot"
 UBOOT_ENV_SUFFIX = "scr"
 
 do_compile_append () {
+    sed -i -e 's/\${platform}/${MACHINE}/g' ${WORKDIR}/bootscript.txt
     uboot-mkimage -A arm -O linux -T script -C none -a 0 -e 0 \
         -n "boot script" -d ${WORKDIR}/bootscript.txt \
         ${WORKDIR}/${UBOOT_ENV_BINARY}