powerpc/64s: Tidy machine check SLB logging

Since ISA v3.0, SLB no longer uses the slb_cache, and stab_rr is no
longer correlated with SLB allocation. Move those to pre-3.0.

While here, improve some alignments and reduce whitespace.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201128070728.825934-9-npiggin@gmail.com