migration: Make savevm.c target independent

It only needed TARGET_PAGE_SIZE/BITS/BITS_MIN values, so just export
them from exec.h

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
5 files changed