rpi-default-versions: Switch default kernel to 5.10
rpi-default-versions: Switch default kernel to 5.10

* 5.10.11 is now considered stable:
  https://github.com/raspberrypi/firmware/blob/stable/extra/uname_string7
  https://github.com/raspberrypi/firmware/commit/8572bb50bf24a9ffef949ced69776e66559f4afe

Signed-off-by: Martin Jansa <516df3ff67e1fa5d153800b15fb204c0a1a389dc@gmail.com>

schnitzeltony/meta-raspberrypi,schnitzeltony/meta-raspberrypi,agherzan/meta-raspberrypi,agherzan/meta-raspberrypi,schnitzeltony/meta-raspberrypi,agherzan/meta-raspberrypi,agherzan/meta-raspberrypi,agherzan/meta-raspberrypi,agherzan/meta-raspberrypi