[SPARC64]: Use ASI_SCRATCHPAD address 0x0 properly.

This is where the virtual address of the fault status
area belongs.

To set it up we don't make a hypervisor call, instead
we call OBP's SUNW,set-trap-table with the real address
of the fault status area as the second argument.  And
right before that call we write the virtual address into
ASI_SCRATCHPAD vaddr 0x0.

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