fuzz: move some DMA hooks

fuzz: move some DMA hooks

For the sparse-mem device, we want the fuzzer to populate entire DMA
reads from sparse-mem, rather than hooking into the individual MMIO
memory_region_dispatch_read operations. Otherwise, the fuzzer will treat
each sequential read separately (and populate it with a separate
pattern). Work around this by rearranging some DMA hooks. Since the
fuzzer has it's own logic to skip accidentally writing to MMIO regions,
we can call the DMA cb, outside the flatview_translate loop.

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>