migration: Create options.c

We move there all capabilities helpers from migration.c.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

---

Following David advise:
- looked through the history, capabilities are newer than 2012, so we
  can remove that bit of the header.
- This part is posterior to Anthony.
  Original Author is Orit. Once there,
  I put myself.  Peter Xu also did quite a bit of work here.
  Anyone else wants/needs to be there?  I didn't search too hard
  because nobody asked before to be added.

What do you think?

migration/savevm.c

@@ -67,6 +67,7 @@
 #include "qemu/yank.h"
 #include "yank_functions.h"
 #include "sysemu/qtest.h"
+#include "options.h"
 
 const unsigned int postcopy_ram_discard_version;