arm/xen: Add support for 64KB page granularity

arm/xen: Add support for 64KB page granularity

The hypercall interface is always using 4KB page granularity. This is
requiring to use xen page definition macro when we deal with hypercall.

Note that pfn_to_gfn is working with a Xen pfn (i.e 4KB). We may want to
rename pfn_gfn to make this explicit.

We also allocate a 64KB page for the shared page even though only the
first 4KB is used. I don't think this is really important for now as it
helps to have the pointer 4KB aligned (XENMEM_add_to_physmap is taking a
Xen PFN).

Signed-off-by: Julien Grall <julien.grall@citrix.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
(cherry picked from commit 250c9af3d831139317009eaebbe82e20d23a581f)
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>