cns3xxx: fix shared PCI interrupt mapping

cns3xxx: fix shared PCI interrupt mapping

This patch originally failed to combine INTA/B/C/D onto a single ARM CPU
interrupt. Instead, it mapped INTA/B/C and excluded D. This patch
corrects the issue by mapping all four interrupts to the single ARM CPU
interrupt. The original intent of the patch still holds as the newer PCB
take advantage of isolated interrupts. This fix only applies to older
PCB's that do not route INTA/B/C/D to unique external ARM CPU
interrupts.

Signed-off-by: Pushpal Sidhu <psidhu@gateworks.com>
Backport of r42830

git-svn-id: svn://svn.openwrt.org/openwrt/branches/barrier_breaker@42846 3c298f89-4303-0410-b956-a3cf2f4a3e73