xen/arm: Check if the platform is not using ACPI before initializing Dom0less

xen/arm: Check if the platform is not using ACPI before initializing Dom0less

Dom0less requires a device-tree. However, since commit 6e3e77120378
"xen/arm: setup: Relocate the Device-Tree later on in the boot", the
device-tree will not get unflatten when using ACPI.

This will lead to a crash during boot.

Given the complexity to setup dom0less with ACPI (for instance how to
assign device?), we should skip any code related to Dom0less when using
ACPI.

Signed-off-by: Julien Grall <jgrall@amazon.com>
Tested-by: Rahul Singh <rahul.singh@arm.com>
Reviewed-by: Rahul Singh <rahul.singh@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Tested-by: Elliott Mitchell <ehem+xen@m5p.com>
(cherry picked from commit dac867bf9adc1562a4cf9db5f89726597af13ef8)