Imagis IST3038 is another variant of Imagis IST3038 IC, which has
a different register interface from IST3038C (possibly firmware defined).
Unlike IST3038C/IST3032C, IST3038 has different registers for commands,
which means IST3038 doesn't use protocol B.
Similar to IST3032C and maybe the other variants, IST3038 has touch keys
support, which provides KEY_APPSELECT and KEY_BACK.
Add support for IST3038 with touch keys.
protocol_b is a property, which tells Imagis panel to use a different
format for coordinates.
IST30XXC series is known for using protocol B, while the other series
aren't. Note this could be confusing, unlike the model name implies.
Adjust the usage of protocol_b to avoid confusion.
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v2: Sort the compatible enties in alphabetical order.
Document the binding before using in the driver.
