bpf: remove the cgroup -> bpf header dependecy

Now that the stage has been set and actors are in place
remove the header dependency between cgroup and bpf.h.

This reduces the incremental build size of x86 allmodconfig
after bpf.h was touched from ~17k objects rebuilt to ~5k objects.
bpf.h is 2.2kLoC and is modified relatively often.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/bpf-cgroup.h

@@ -2,7 +2,8 @@
 #ifndef _BPF_CGROUP_H
 #define _BPF_CGROUP_H
 
-#include <linux/bpf.h>
+#include <linux/bpf-cgroup-types.h>
+#include <linux/bpf-link.h>
 #include <linux/errno.h>
 #include <linux/jump_label.h>
 #include <linux/percpu.h>
@@ -16,6 +17,7 @@ struct cgroup;
 struct sk_buff;
 struct bpf_map;
 struct bpf_prog;
+struct bpf_prog_aux;
 struct bpf_sock_ops_kern;
 struct bpf_cgroup_storage;
 struct ctl_table;