migration: Convert ram to use new load_setup()/load_cleanup()

Once there, I rename ram_migration_cleanup() to ram_save_cleanup().
Notice that this is the first pass, and I only passed XBZRLE to the
new scheme.  Moved decoded_buf to inside XBZRLE struct.
As a bonus, I don't have to export xbzrle functions from ram.c.

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

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loaded_data pointer was needed because called can change it (dave)
spell loaded correctly in comment (dave)
Message-Id: <20170628095228.4661-5-quintela@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>