rpi-default-versions: Switch defaults to 5.4
rpi-default-versions: Switch defaults to 5.4

Linux Kernel 5.4 is now considered stable.

See [1] to check the current apt stable kernel.

[1] - https://github.com/raspberrypi/firmware/blob/stable/extra/uname_string7

Signed-off-by: Pierre-Jean Texier <188dcb29e125b35642aafd9b1cc33149502c1da3@koncepto.io>

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