bpftool: recognize BPF_PROG_TYPE_CGROUP_DEVICE programs

Bpftool doesn't recognize BPF_PROG_TYPE_CGROUP_DEVICE programs,
so the prog show command prints the numeric type value:

$ bpftool prog show
1: type 15  name bpf_prog1  tag ac9f93dbfd6d9b74
	loaded_at Jan 15/07:58  uid 0
	xlated 96B  jited 105B  memlock 4096B

This patch defines the corresponding textual representation:

$ bpftool prog show
1: cgroup_device  name bpf_prog1  tag ac9f93dbfd6d9b74
	loaded_at Jan 15/07:58  uid 0
	xlated 96B  jited 105B  memlock 4096B

Signed-off-by: Roman Gushchin <guro@fb.com>
Cc: Jakub Kicinski <jakub.kicinski@netronome.com>
Cc: Quentin Monnet <quentin.monnet@netronome.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Alexei Starovoitov <ast@kernel.org>
Acked-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>