MIPS: IP27: Fix build errors with CONFIG_PCI disabled.

MIPS: IP27: Fix build errors with CONFIG_PCI disabled.

  LD      init/built-in.o
arch/mips/built-in.o: In function `xtalk_probe_node':
(.cpuinit.text+0x67c): undefined reference to `bridge_probe'
arch/mips/built-in.o: In function `xtalk_probe_node':
(.cpuinit.text+0x7d8): undefined reference to `bridge_probe'

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>