meta-agl-bsp: meta-raspberrypi updates for YP 3.1.2

meta-agl-bsp: meta-raspberrypi updates for YP 3.1.2

Changes include:
- Rename bcm2835-bootfiles.bbappend to bootfiles.bbappend to match
  the recipe rename done in meta-raspberrypi
- Update bootfile paths in rpi-config_git.bbappend to match the rename
  done in meta-raspberrypi
- Remove local u-boot bbappend, as none of its changes are required
  with latest meta-raspberrypi and meta-updater
- A previously silently failing command in the create-combined-dtb
  recipe's do_install when building with agl-sota enabled now triggers
  a build failure, logic has been added to handle meta-updater's
  disabling of the required overlay file.

Bug-AGL: SPEC-3529

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: Ib5fd9f308fcd2da76ae882dd5b2413e56d3eee40
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/25081
Tested-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>