powerpc/pseries/eeh: Refactor the configure_bridge RTAS tokens

The RTAS calls "ibm,configure-pe" and "ibm,configure-bridge" perform the
same actions, however the former can skip configuration if unnecessary.
The existing code treats them as different tokens even though only one
will ever be called.  Refactor this by making a single token that is
assigned during init.

Signed-off-by: Russell Currey <ruscur@russell.cc>
Acked-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>