imx6q_sabrelite_setup_lava: Set u-boot url to persistent location

Sabrelite u-boot includes recent critical fixes, so the required image
version needs to be specified in the lava setup to be installed.

Signed-off-by: Ariel D'Alessandro <ariel.dalessandro@collabora.com>

content/reference_hardware/imx6q_sabrelite_setup_lava.md

@@ -25,6 +25,10 @@ persistent bootloader in the SPI memory to download and write an OS
 image on the SD card, then reboot automatically a second time from the
 SD card with the freshly flashed image.
 
+  - Download the following U-Boot image installer
+  [uboot-v2023dev2-installer-mx6qsabrelite-20220511.0019.img.gz](https://images.apertis.org/lava/boot/mx6qsabrelite/uboot-v2023dev2-installer-mx6qsabrelite-20220511.0019.img.gz). Note that other related files to this image, e.g. bmap file, can be downloaded as well from
+  [here](https://images.apertis.org/lava/boot/mx6qsabrelite/).
+
   - Follow the instructions [developer
     instructions]( {{< ref "/reference_hardware/imx6q_sabrelite_setup.md" >}} )
     to get U-Boot installed on the SABRE Lite.