[SPARC64]: Set %gl to 1 in kvmap_itlb_longpath on SUN4V.

Just like kvmap_dtlb_longpath we have to force the
global register level to one in order to mimick the
PSTATE_MG --> PSTATE_AG trasition done on SUN4U.

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