perf bpf-filter: Improve error messages

perf bpf-filter: Improve error messages

The BPF filter needs libbpf/BPF-skeleton support and root privilege.
Add error messages to help users understand the problem easily.

When it's not build with BPF support (make BUILD_BPF_SKEL=0).

  $ sudo perf record -e cycles --filter "pid != 0" true
  Error: BPF filter is requested but perf is not built with BPF.
  	Please make sure to build with libbpf and BPF skeleton.

   Usage: perf record [<options>] [<command>]
      or: perf record [<options>] -- <command> [<options>]

          --filter <filter>
                            event filter

When it supports BPF but runs without root or CAP_BPF.  Note that it
also checks pinned BPF filters.

  $ perf record -e cycles --filter "pid != 0" -o /dev/null true
  Error: BPF filter only works for users with the CAP_BPF capability!
  	Please run 'perf record --setup-filter pin' as root first.

   Usage: perf record [<options>] [<command>]
      or: perf record [<options>] -- <command> [<options>]

          --filter <filter>
                            event filter

Reviewed-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20250604174835.1852481-1-namhyung@kernel.org
Signed-off-by: Namhyung Kim <namhyung@kernel.org>