Load instructions using ASI_PNF or other no-fault ASIs should not
cause a SIGSEGV or SIGBUS.

A garden variety unmapped address follows the TSB miss path, and when
no valid mapping is found in the process page tables, the miss handler
checks to see if the access was via a no-fault ASI.  It then fixes up
the target register with a zero, and skips the no-fault load
instruction.

But different paths are taken for data access exceptions and alignment
traps, and these do not respect the no-fault ASI. We add checks in
these paths for the no-fault ASI, and fix up the target register and
TPC just like in the TSB miss case.

Signed-off-by: Rob Gardner <rob.gardner@oracle.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>