kbuild,bpf: Switch to using --btf_features for pahole v1.26 and later

The btf_features list can be used for pahole v1.26 and later -
it is useful because if a feature is not yet implemented it will
not exit with a failure message.  This will allow us to add feature
requests to the pahole options without having to check pahole versions
in future; if the version of pahole supports the feature it will be
added.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Tested-by: Eduard Zingerman <eddyz87@gmail.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240507135514.490467-1-alan.maguire@oracle.com