linux-postmarketos-qcom-msm8916: upgrade to 6.12.1 (MR 5847)

- Update to Linux v6.12.1
- Lots of cleanup and upstreaming, more than 30 commits upstreamed since 6.7
- Various defconfig updates

Device changes:
  - Acer a1-724 gains sound/modem, mount-matrix, simple-framebuffer display
  - L8910/l9100 (BQ Aquaris X5/M5) gain rgb led
  - More variants of Lenovo Vibe K5 supported
  - grandmax gains touchkeys
  - heatqlte gains backlight
  - gplus fl8005a gains modem, display, battery
  - serranove gains hardware-side display flip and brightness control

New devices:
  - Fareastone Smart 506
  - Lenovo Yoga Tab 3 10 LTE
  - Vivo Y21L
  - ZTE N818s (sapphire)