x86/xen: discard RAM regions above the maximum reservation

During setup, discard RAM regions that are above the maximum
reservation (instead of marking them as E820_UNUSABLE).  This allows
hotplug memory to be placed at these addresses.
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

arch/x86/xen/setup.c

@@ -829,6 +829,8 @@ char * __init xen_memory_setup(void)
 	addr = xen_e820_map[0].addr;
 	size = xen_e820_map[0].size;
 	while (i < xen_e820_map_entries) {
+		bool discard = false;
+
 		chunk_size = size;
 		type = xen_e820_map[i].type;
 
@@ -843,9 +845,10 @@ char * __init xen_memory_setup(void)
 				xen_add_extra_mem(pfn_s, n_pfns);
 				xen_max_p2m_pfn = pfn_s + n_pfns;
 			} else
-				type = E820_UNUSABLE;
+				discard = true;
 		}
 
+		if (!discard)
 			xen_align_and_add_e820_region(addr, chunk_size, type);
 
 		addr += chunk_size;