pseries: Allow TCG h_enter to work with hotplugged memory

The implementation of the H_ENTER hypercall for PAPR guests needs to
enforce correct access attributes on the inserted HPTE.  This means
determining if the HPTE's real address is a regular RAM address (which
requires attributes for coherent access) or an IO address (which requires
attributes for cache-inhibited access).

At the moment this check is implemented with (raddr < machine->ram_size),
but that only handles addresses in the base RAM area, not any hotplugged
RAM.

This patch corrects the problem with a new helper.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
