powerpc/64: Add logical PVR to the hardware description

If we detect a logical PVR add that to the hardware description, which
is printed at boot and in case of an oops.

eg: Hardware name: ... 0xf000004

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220930082709.55830-3-mpe@ellerman.id.au