BeagleBone Black: let the default FW "boot from the SD card"

I just don't want to hold that button at each power-up, and I have not
added support for flashing to eMMC yet. The default, preinstalled
bootlaoder tries to read uEnv.txt from the SDD card's boot partition and
execute `uenvcmd` from there, so let's make it happy and adapt
ourselves.

The default U-Boot installed on-device (2015.01-00001-gb2412df) doesn't
define ${scriptaddr}, so we have to provide it if we want our launchers
to succeed.

Change-Id: I50dc5177f4dd16435d4f5d17908db938e4cc5c3c
diff --git a/board/czechlight/beaglebone/create-uEnv.sh b/board/czechlight/beaglebone/create-uEnv.sh
index 9808fdd..3e0c513 100755
--- a/board/czechlight/beaglebone/create-uEnv.sh
+++ b/board/czechlight/beaglebone/create-uEnv.sh
@@ -2,6 +2,8 @@
 
 install -m 0644 -D $BINARIES_DIR/boot.scr $TARGET_DIR/boot/boot.scr
 
+cp ${BR2_EXTERNAL_CZECHLIGHT_PATH}/board/czechlight/beaglebone/sd-uEnv.txt ${BINARIES_DIR}/
+
 # prepare the static script with RAUC logic
 ${HOST_DIR}/bin/mkimage -C none -A arm -T script \
         -d ${BR2_EXTERNAL_CZECHLIGHT_PATH}/board/czechlight/beaglebone/rauc.scr.txt ${BINARIES_DIR}/rauc.scr