xen: Don't try to call xen_alloc_p2m_entry() on autotranslating guests

Commit aba831a69632 ("xen: remove tests for pvh mode in pure pv paths")
removed XENFEAT_auto_translated_physmap test in xen_alloc_p2m_entry()
since it is assumed that the routine is never called by non-PV guests.

However, alloc_xenballooned_pages() may make this call on a PVH guest.
Prevent this from happening by adding XENFEAT_auto_translated_physmap
check there.

Signed-off-by: Boris Ostrovsky <[e-mail]>
Reviewed-by: Juergen Gross <[e-mail]>
Fixes: aba831a69632 ("xen: remove tests for pvh mode in pure pv paths")

drivers/xen/balloon.c

···
 			 */
 			BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
 
-			ret = xen_alloc_p2m_entry(page_to_pfn(page));
-			if (ret < 0)
-				goto out_undo;
+			if (!xen_feature(XENFEAT_auto_translated_physmap)) {
+				ret = xen_alloc_p2m_entry(page_to_pfn(page));
+				if (ret < 0)
+					goto out_undo;
+			}
 #endif
 		} else {
 			ret = add_ballooned_pages(nr_pages - pgno);