kbuild, bpf: Use test-ge check for v1.25-only pahole

kbuild, bpf: Use test-ge check for v1.25-only pahole

There is no need to set the pahole v1.25-only flags in an
"ifeq" version clause; we are already in a <= v1.25 branch
of "ifeq", so that combined with a "test-ge" v1.25 ensures the
flags will be applied for v1.25 only.

Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240514162716.2448265-1-alan.maguire@oracle.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>