staging: hikey9xx: add a TODO list

Place the things that are needed to be able to move those
drivers out of staging.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/bf3ebe32125646e0a87a59280392e8c6fda08488.1597647359.git.mchehab+huawei@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/hikey9xx/TODO

+ToDo list:
+
+- Port other drivers needed by Hikey 960/970;
+- Test drivers on Hikey 960;
+- Validate device tree bindings.