xen/arm: dt: Relax hw domain mapping attributes to p2m_mmio_direct_c

xen/arm: dt: Relax hw domain mapping attributes to p2m_mmio_direct_c

Since the hardware domain is a trusted domain, we extend the
trust to include making final decisions on what attributes to
use when mapping memory regions.

For device-tree configured hardware domains, this patch relaxes
the hardware domains mapping attributes to p2m_mmio_direct_c.
This will allow the hardware domain to control the attributes
via its S1 mappings.

Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Reviewed-by: Julien Grall <julien.grall@arm.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>