cadence_gem: Fix priority queue out of bounds access

There was an error with some of the register implementation assuming
there are 16 priority queues supported when the IP only supports 8. This
patch corrects the registers to only support 8 queues.

Signed-off-by: Alistair Francis <alistair.francis@xilinx.com>
Reported-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 33bf2d28326d22875602234b8b15cf56fb678333.1474911607.git.alistair.francis@xilinx.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
