powerpc/mm: Update definitions of DSISR bits

This updates the definitions for the various DSISR bits to
match both some historical stuff and to match new bits on
POWER9.

In addition, we define some masks corresponding to the "bad"
faults on Book3S, and some masks corresponding to the bits
that match between DSISR and SRR1 for a DSI and an ISI.

This comes with a small code update to change the definition
of DSISR_PGDIRFAULT which becomes DSISR_PRTABLE_FAULT to
match architecture 3.0B

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>