iio: add a TODO

This patch adds a TODO file with some work items added with reference to
the conversation in [1].
A TODO file is immensely useful while onboarding new contributors who
are looking for some low hanging fruit to get their foot into the door.
Since these items affect all drivers the file has been placed in the
root iio directory instead of augmenting the staging TODO.

Thanks,
Rohit

[1]: https://marc.info/?l=linux-iio&m=158256721009892&w=2Signed-off-by: Rohit Sarkar <rohitsarkar5398@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/TODO

+2020-02-29
+
+Documentation
+  - Binding docs for devices that are obviously used via device
+tree
+  - Yaml conversions for abandoned drivers
+  - ABI Documentation
+  - Audit driviers/iio/staging/Documentation
+
+- Replace iio_dev->mlock by either a local lock or use
+iio_claim_direct.(Requires analysis of the purpose of the lock.)
+
+- Converting drivers from device tree centric to more generic
+property handlers.
+
+- Refactor old platform_data constructs from drivers and convert it
+to state struct and using property handlers and readers.
+
+Mailing list: linux-iio@vger.kernel.org