drm: kirin: Fix for hikey620 display offset problem

The original HiKey (620) board has had a long running issue
where when using a 1080p montior, the display would occasionally
blink and come come back with a horizontal offset (usually also
shifting the colors, depending on the value of the offset%4).

After lots of analysis by HiSi developers, they found the issue
was due to when running at 1080p, it was possible to hit the
device memory bandwidth limits, which could cause the DSI signal
to get out of sync.

Unfortunately the DSI logic doesn't have the ability to
automatically recover from this situation, but we can get a an
LDI underflow interrupt when it happens.

To then correct the issue, when we get an LDI underflow irq, we
we can simply suspend and resume the display, which resets the
hardware.

Thus, this patch enables the ldi underflow interrupt, and
initializes a workqueue that is used to suspend/resume the
display to recover. Then when the irq occurs we clear it and
schedule the workqueue to reset display engine.

Cc: Rongrong Zou <zourongrong@gmail.com>
Cc: Xinliang Liu <z.liuxinliang@hisilicon.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel <dri-devel@lists.freedesktop.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Xinliang Liu <z.liuxinliang@hisilicon.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Da Lv <lvda3@hisilicon.com>
Signed-off-by: Yidong Lin <linyidong@huawei.com>
[jstultz: Reworded the commit message, checkpatch cleanups]
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190820230626.23253-2-john.stultz@linaro.org