Including libbpf header files should be guarded by HAVE_LIBBPF_SUPPORT.
In bpf_counter.h, move the skeleton utilities under HAVE_BPF_SKEL.

Fixes: d6a735ef ("perf bpf_counter: Move common functions to bpf_counter.h")
Reported-by: NMike Leach <mike.leach@linaro.org>
Signed-off-by: NIan Rogers <irogers@google.com>
Tested-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Tested-by: NJiri Olsa <jolsa@kernel.org>
Tested-by: NMike Leach <mike.leach@linaro.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20230105172243.7238-1-mike.leach@linaro.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>