powerpc/cell: tidy up pervasive declarations

These are declared in ras.h and defined in ras.c so remove them from
pervasive.h

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210130130852.2952424-23-npiggin@gmail.com