cadence_gem: Flush queued packets

The device needs to check for queued RX packets when the RX path is re-enabled.

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Message-id: 1fa8c88a3b7c654886d0a7484c2463cd4c2a2781.1360901435.git.peter.crosthwaite@xilinx.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
