x86/altp2m: Add a subop for obtaining the mem access of a page

x86/altp2m: Add a subop for obtaining the mem access of a page

Currently there is a subop for setting the memaccess of a page, but not
for consulting it.  The new HVMOP_altp2m_get_mem_access adds this
functionality.

Both altp2m get/set mem access functions use the struct
xen_hvm_altp2m_mem_access which has now dropped the `set' part and has
been renamed from xen_hvm_altp2m_set_mem_access.

Signed-off-by: Adrian Pop <apop@bitdefender.com>
Signed-off-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Tamas K Lengyel <tamas@tklengyel.com>
Reviewed-by: George Dunlap <george.dunlap@citrix.com>