kvm tools: Remember page size as kvm->ram_pagesize

kvm tools: Remember page size as kvm->ram_pagesize

On some powerpc platforms we need to make sure we only advertise page
sizes to the guest which are <= the size of the pages backing guest RAM.

So have mmap_hugetblfs() save the hugetblfs page size for us, and also
teach mmap_anon_or_hugetblfs() to set the page size for anonymous mmap.

Acked-by: Matt Evans <matt@ozlabs.org>
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Pekka Enberg <penberg@kernel.org>