bpf: fix build issues on um due to mising bpf_perf_event.h

Since c895f6f7 ("bpf: correct broken uapi for
BPF_PROG_TYPE_PERF_EVENT program type") um (uml) won't build
on i386 or x86_64:

  [...]
    CC      init/main.o
  In file included from ../include/linux/perf_event.h:18:0,
                   from ../include/linux/trace_events.h:10,
                   from ../include/trace/syscall.h:7,
                   from ../include/linux/syscalls.h:82,
                   from ../init/main.c:20:
  ../include/uapi/linux/bpf_perf_event.h:11:32: fatal error:
  asm/bpf_perf_event.h: No such file or directory #include
  <asm/bpf_perf_event.h>
  [...]

Lets add missing bpf_perf_event.h also to um arch. This seems
to be the only one still missing.

Fixes: c895f6f7 ("bpf: correct broken uapi for BPF_PROG_TYPE_PERF_EVENT program type")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Suggested-by: Richard Weinberger <richard@sigma-star.at>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Cc: Richard Weinberger <richard@sigma-star.at>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

arch/um/include/asm/Kbuild

 generic-y += barrier.h
+generic-y += bpf_perf_event.h
 generic-y += bug.h
 generic-y += clkdev.h
 generic-y += current.h