powerpc: Add PVR & CPU name to hardware description

Add the PVR and CPU name to the hardware description, which is printed
at boot and in case of an oops.

eg: Hardware name: ... POWER8E (raw) 0x4b0201

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220930082709.55830-2-mpe@ellerman.id.au