During board bringups its useful to have a DSI test pattern
generator to isolate a DPU vs a DSI issue and focus on the relevant
hardware block.

To facilitate this, add an API which triggers the DSI controller
test pattern. The expected output is a rectangular checkered pattern.

This has been validated on a single DSI video mode panel by calling it
right after drm_panel_enable() which is also the ideal location to use
this as the DSI host and the panel have been initialized by then.

Further validation on dual DSI and command mode panel is pending.
If there are any fix ups needed for those, it shall be applied on top
of this change.

Changes in v2:
 - generate the new dsi.xml.h and update the bitfield names
Signed-off-by: Abhinav Kumar <abhinavk@codeaurora.org>
Link: https://lore.kernel.org/r/1626922232-29105-2-git-send-email-abhinavk@codeaurora.orgReviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>