sensors: cirque: add dpad-mode

[JohSchneider]

Inspired by game controllers that use a circular touchpad instead of an analog joystick or a directional pad. This adds the later, which does the following: splitting the touchpad area into quadrants = "virtual keys", that emit a key press event when a touch-down event in that segment is registered. A key release event is emitted when a "touch up" happens, or the touch event leaves the respective segment.

There is also a software switchable "blend mode" that, unlike the discrete mode, allows two adjacent keys to be pressed - to for example enable diagonal movement, when the four cursor keys are mapped to the virtual dpad.

The key-codes for the four virtual buttons are taken from an additional row in the keymap; the row number put into a define and then used by the dpad feature to trigger the key.

Description

Types of Changes

• [ ] Core
• [ ] Bugfix
• [x] New feature
• [ ] Enhancement/optimization
• [ ] Keyboard (addition or update)
• [ ] Keymap/layout/userspace (addition or update)
• [x] Documentation

Issues Fixed or Closed by This PR

Checklist

• [ ] My code follows the code style of this project: C, Python
• [x] I have read the PR Checklist document and have made the appropriate changes.
• [ ] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [x] I have tested the changes and verified that they work and don't break anything (as well as I can manage).