xen/arm: setup: Add Xen as boot module before printing all boot modules

xen/arm: setup: Add Xen as boot module before printing all boot modules

Since commit f60658c6ae "xen/arm: Stop relocating Xen", the position of
Xen in memory is not printed anymore. This can make difficult to debug
early code.

As Xen is not relocated anymore, we can add Xen as boot module before
calling boot_fdt_info(). With that, the function will print Xen module
information along with all the other modules.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>