powerpc: GE Fanuc's FPGA based PIC controller on the SBC610

Support for the SBC610 VPX Single Board Computer from GE Fanuc (PowerPC MPC8641D).

A number of MPC8641D based route interrupts for on-board interrupts through
a FPGA based interrupt controller, which is chained with the
MPC8641D's mpic. This patch provides a basic driver to allow basic routing
of interrupts to the mpic.

Signed-off-by: Martyn Welch <martyn.welch@gefanuc.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>