xen: arm: allow virt_to_maddr to take either a pointer or an integer

xen: arm: allow virt_to_maddr to take either a pointer or an integer

This seems to be expected by common code which passes both pointers and
unsigned long as virtual addresses. The latter case in particular is in
init_node_heap() under a DIRECTMAP_VIRT_END #ifdef, which is why it hasn't
affected us yet (but will in a subsequent patch).

The new prototypes match the x86 versions apart from using vaddr_t instead of
unsigned long.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>