xen/arm, device-tree: Make static-mem use #{address,size}-cells

xen/arm, device-tree: Make static-mem use #{address,size}-cells

In order to keep consistency in the device tree binding, there is
no need for static memory allocation feature to define a specific
set of address and size cells for "xen,static-mem" property.

Therefore, this commit reuses the regular #{address,size}-cells
for parsing the device tree "xen,static-mem" property. Update
the documentation accordingly.

Also, take the chance to remove the unnecessary "#address-cells"
and "#size-cells" in the domU1 node of the device tree to only
emphasize the related part that the example is showing.

Signed-off-by: Henry Wang <Henry.Wang@arm.com>
Reviewed-by: Michal Orzel <michal.orzel@amd.com>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>