perf: Version String fix, for fallback if not from git

This gets rid of the default version fallback for Perf and
changes it so that it returns the version of the kernel from
it's Makefile (if sources were not from git, ie. if it was
downloaded from a tarball)

Signed-off-by: Thavidu Ranatunga <tharan@au1.ibm.com>
Acked-by: Ian Munsie <imunsie@au1.ibm.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <1278316815-6099-2-git-send-email-tharan@au1.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>