[SPARC64] PCI: Size TSB correctly on SUN4V.

Forgot to multiply by 8 * 1024, oops.  Correct the size constant when
the virtual-dma arena is 2GB in size, it should bet 256 not 128.

Finally, log some info about the TSB at probe time.

Signed-off-by: David S. Miller <davem@davemloft.net>