[SPARC64]: Simplify sun4v TLB handling using macros.

There was also a bug in sun4v_itlb_miss, it loaded the
MMU Fault Status base into %g3 instead of %g2.

This pointed out a fast path for TSB miss processing,
since we have %g2 with the MMU Fault Status base, we
can use that to quickly load up the PGD phys address.

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