According to:
https://www.kernel.org/category/releases.html
version 5.4 is a longterm release, so:
- add longterm 5.4 series at 5.4.18
- update longterm 4.19 series to 4.19.103
- update stable to 5.5.3
- remove rc, as it quickly gets out of date. rc users will likely build
kernel from master outside of OE anyway
- set 5.4 as the preferred version for linux-mainline
Signed-off-by: Diego Rondini <diego.rondini@kynetics.com>
