upsquared6000: Download grub from collabora lava gitlab job

The UP Squared 6000 board needs an updated version of grub, which is
built and available in the collabora lava gitlab repositories.

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

content/reference_hardware/upsquared6000_setup_lava.md

@@ -32,21 +32,11 @@ binary. There should already be a TFTP server installed as part of the LAVA
 dispatcher set-up. The same server can be used to provide the PXE boot binary
 (GRUB).
 
-Create a directory on the dispatcher:
+Create directory `/srv/tftp/lava-grub2/x86_64-efi/` on the dispatcher and
+download the [latest GRUB binary](https://gitlab.collabora.com/lava/grub/-/jobs/artifacts/master/raw/core.efi?job=build-amd64)
+to it.
 
-```
-$ mkdir -p /srv/tftp/lava-grub2/x86_64-efi/
-```
-
-Install the GRUB binary with all the required modules built-in in this
-directory:
-
-```
-$ cd /srv/tftp/lava-grub2/x86_64-efi/
-$ wget https://images.collabora.co.uk/lava/boot/lava-grub2/x86_64-efi/core.efi
-```
-
-Note: To build GRUB (`core.efi` mentioned above) from source:
+Note: To build the GRUB binary (`core.efi`) from source:
 
 ```
 $ git clone https://gitlab.collabora.com/lava/grub.git