x86/hvm: allow XENMEM_machine_memory_map

For HVM based control domains XENMEM_machine_memory_map must be available so
that the `e820_host` xl.cfg option can be used.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/hvm/hypercall.c

@@ -25,7 +25,6 @@ long hvm_memory_op(unsigned long cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
 
     switch ( cmd & MEMOP_CMD_MASK )
     {
-    case XENMEM_machine_memory_map:
     case XENMEM_machphys_mapping:
         return -ENOSYS;
     }