bpf: Fix warning for bpf_cpumask in verifier

Compiling with CONFIG_BPF_SYSCALL & !CONFIG_BPF_JIT throws the below
warning:

  "WARN: resolve_btfids: unresolved symbol bpf_cpumask"

Fix it by adding the appropriate #ifdef.
Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Stanislav Fomichev <sdf@google.com>
Acked-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/bpf/20240208100115.602172-1-hbathini@linux.ibm.com

kernel/bpf/verifier.c

@@ -5227,7 +5227,9 @@ BTF_ID(struct, prog_test_ref_kfunc)
 #ifdef CONFIG_CGROUPS
 BTF_ID(struct, cgroup)
 #endif
+#ifdef CONFIG_BPF_JIT
 BTF_ID(struct, bpf_cpumask)
+#endif
 BTF_ID(struct, task_struct)
 BTF_SET_END(rcu_protected_types)