powerpc/cpm2_pic: Allow correct flow_types for port C interrupts

Port C interrupts can be either falling edge, or either edge.
Other external interrupts are either falling edge or active low.
Tested on a custom 8280 based board.

Signed-off-by: Mark Ware <mware@elphinstone.net>
Acked-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Acked-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>