perf: Add util/include/linuxhash.h to include hash.h of kernel

linux/hash.h, hash header of kernel, is also useful for perf.

util/include/linuxhash.h includes linux/hash.h, so we can use
hash facilities (e.g. hash_long()) in perf now.

Signed-off-by: Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <1264851813-8413-3-git-send-email-mitake@dcl.info.waseda.ac.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>