perf powerpc: Fix build-test failure

perf powerpc: Fix build-test failure

'make -C tools/perf build-test' is failing with below log for poewrpc.

  In file included from /tmp/tmp.3eEwmGlYaF/perf-4.8.0-rc4/tools/perf/perf.h:15:0,
                   from util/cpumap.h:8,
                   from util/env.c:1:
  /tmp/tmp.3eEwmGlYaF/perf-4.8.0-rc4/tools/perf/perf-sys.h:23:56:
  fatal error: ../../arch/powerpc/include/uapi/asm/unistd.h: No such file or directory
  compilation terminated.

I bisected it and found it's failing from commit ad430729ae00 ("Remove:
kernel unistd*h files from perf's MANIFEST, not used").

Header file '../../arch/powerpc/include/uapi/asm/unistd.h' is included
only for powerpc in tools/perf/perf-sys.h.

By looking closly at commit history, I found little weird thing:

Commit f2d9cae9ea9e ("perf powerpc: Use uapi/unistd.h to fix build
error") replaced 'asm/unistd.h' with 'uapi/asm/unistd.h'

Commit d2709c7ce4c5 ("perf: Make perf build for x86 with UAPI
disintegration applied") removes all arch specific 'uapi/asm/unistd.h'
for all archs and adds generic <asm/unistd.h>.

Commit f0b9abfb0446 ("Merge branch 'linus' into perf/core") again
includes 'uapi/asm/unistd.h' for powerpc. Don't know how exactly this
happened as this change is not part of commit also.

Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1472630591-5089-1-git-send-email-ravi.bangoria@linux.vnet.ibm.com
Fixes: ad430729ae00 ("Remove: kernel unistd*h files from perf's MANIFEST, not used")
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>