xen/arm: Provide device tree debugging helper in a single place

xen/arm: Provide device tree debugging helper in a single place

Provide helper to debug the device tree in device_tree.h. This will
avoid to have to redeclare helper for each file requiring debug.

Also replace DPRINT by the new helper dt_dprintk in domain_build.c

Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>