xen: arm: map entire memory banks on arm64

xen: arm: map entire memory banks on arm64

Currently we only map regions which are not part of boot modules. However we
subsequently free at least some of those modules to the heaps in
discard_initial_modules and if we were unluckly with sizing/location we might
end up adding unmapped pages to the heap.

The heaps on 64-bit use 1GB mappings, so in practice this is probably pretty
unlikely and I've not actually seen it.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Julien Grall <julien.grall@linaro.org>