This drops kernel version switches for versions not supported by
OpenWrt master at the moment. This only adjusts local code, but
doesn't touch patches to existing external packages.
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
The SUBDIRS variable has been removed in kernel 5.4, and was deprecated
since the beginnig of kernel git history in favour of M or KBUILD_EXTMOD.
Signed-off-by: Tomasz Maciej Nowak <tomek_n@o2.pl>