package Makefile: fix perf-tar targets when outdir is set

building with $srctree != $objtree, perf-tar-* targets fail
to read the MANIFEST file and add the PERF-VERSION-FILE needed
by out-of-tree builds. The build errors and an incorrect tar is created:

$ make O=build-x86 perf-targz-src-pkg
  TAR
cat: ../tools/perf/MANIFEST: No such file or directory
tar: perf-4.1.0-rc8/PERF-VERSION-FILE: Cannot stat: No such file or
dir..
tar: Exiting with failure status due to previous errors

Kbuild sets objtree to "." and srctree to ".." The command to output
MANIFEST becomes:

   $(cd ..; echo $(cat ../tools/perf/MANIFEST))

Without MANIFEST, the entire kernel source tree is added to the perf
source tarball. The *correct* fix is to keep the cd and remove srctree
from cat command line since MANIFEST has wildcards that fail to expand
working directory isn't srctree.

Second, PERF-VERSION-FILE gets not added, because in-tree build path is
hardcoded to Makefile:

   util/PERF-VERSION-GEN ../../$(perf-tar)/ 2>/dev/null)
...