[POWERPC] Add cputable entry for PowerPC 440SPe Rev. B

When adding the cputable entry for 440SPe Rev. B, we also need to
adjust the existing entries for 440SP Rev. A and 440SPe Rev. B so that
they look more bits of the PVR.  The 440SPe Rev. B has PVR 53421891,
which would match the current 440SP Rev. A pattern of 53xxx891.  To
distinguish between 440SP and 440SPe, we need to use the first three
digits of the PVR, which are respectively 532 and 534.

Signed-off-by: Roland Dreier <rolandd@cisco.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>