x86: rename p2m_mmio_write_dm to p2m_ioreq_server

x86: rename p2m_mmio_write_dm to p2m_ioreq_server

Previously p2m type p2m_mmio_write_dm was introduced for write-
protected memory pages whose write operations are supposed to be
forwarded to and emulated by an ioreq server. Yet limitations of
rangeset restrict the number of guest pages to be write-protected.

This patch replaces the p2m type p2m_mmio_write_dm with a new name:
p2m_ioreq_server, which means this p2m type can be claimed by one
ioreq server, instead of being tracked inside the rangeset of ioreq
server. And a new memory type, HVMMEM_ioreq_server, is now used in
the HVMOP_set/get_mem_type interface to set/get this p2m type.

Patches following up will add the related HVMOP handling code which
map/unmap type p2m_ioreq_server to/from an ioreq server. Without
following patches, memory type changes to HVMMEM_ioreq_server can
still be allowed, and in such cases, p2m_ioreq_server pages will be
treated the same as ones with previous type p2m_mmio_write_dm, and
are tracked inside the ioreq server's rangeset.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
Acked-by: Tim Deegan <tim@xen.org>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: George Dunlap <george.dunlap@citrix.com>