[PATCH] powerpc: fixing compile issue with !CONFIG_PCI in legacy_serial.c

Only build in support for ISA and PCI cases if we have enabled CONFIG_ISA
and CONFIG_PCI.  Additionally, isa_bridge is a global so we shouldn't use
it a parameter name since it gets redefined to NULL when !CONFIG_PCI.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>