linux-imx

gpu: imx: dpu: framegen: Add helpers to get/clear sec chan status

This patch adds two helpers to get and clear FrameGen secondary channel
status respectively.  Via the two helpers, users may know if there is
empty FIFO read request on this channel or not after getting the status.
And, if yes, users may choose to clear the status.  According to the IP
spec, the empty FIFO read request indicates that data stream from a Fetch
unit(e.g., AXI bandwidth not sufficient) fell down.  Assuming the display
driver sets things up properly, the falling down is very likely caused by
the insufficient AXI bandwidth, that is, display underrun.

Signed-off-by: Liu Ying <victor.liu@nxp.com>