main/linux-postmarketos-qcom-msm8916: upgrade to 5.6-rc2 (!970)

- Update to Linux 5.6-rc2
- Major improvements for Motorola Moto G4 Play (motorola-harpia)
  - Display
  - Touchscreen
  - Accelerometer
  - Audio
  - Modem
  - Vibrator

- Fix headphones/headset detection for wileyfox-crackling
- Add mount-matrix for samsung-a3ulte/a5ulte to fix
  orientation detection with iio-sensor-proxy
- A lot of cleanup everywhere

- APKBUILD: Clean up makedepends (a lot of them are unneeded)