find_ram_offset optimization

The ram_offset allocator searches the smalest gap in the ram_offset address space.
This is slow especialy in combination with many allocation (i.e. snapshots). When
it is known that there is no gap, this is now optimized.

include/qemu.h

@@ -41,6 +41,7 @@ typedef struct {
 
 // This struct is originally from qemu/include/exec/ramlist.h
 typedef struct RAMList {
+    bool freed;
     RAMBlock *mru_block;
     QLIST_HEAD(, RAMBlock) blocks;
 } RAMList;