MAINTAINERS: Add btf headers to BPF

BPF folks maintain these and they're not picked up by the current
MAINTAINERS entries.

Files caught by the added globs:

  include/linux/btf.h
  include/linux/btf_ids.h
  include/uapi/linux/btf.h
Signed-off-by: NDave Marchevsky <davemarchevsky@fb.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210924193557.3081469-1-davemarchevsky@fb.com

MAINTAINERS

@@ -3379,9 +3379,11 @@ F:	Documentation/networking/filter.rst
 F:	Documentation/userspace-api/ebpf/
 F:	arch/*/net/*
 F:	include/linux/bpf*
+F:	include/linux/btf*
 F:	include/linux/filter.h
 F:	include/trace/events/xdp.h
 F:	include/uapi/linux/bpf*
+F:	include/uapi/linux/btf*
 F:	include/uapi/linux/filter.h
 F:	kernel/bpf/
 F:	kernel/trace/bpf_trace.c