perf annotate: Add missing powerpc triplet

On an Ubuntu xenial system, 'perf annotate' says to install powerpc
objdump on a system that already has binutils-powerpc-linux-gnu
installed.  Make perf aware of the missing triplet for the
powerpc-linux-gnu target.

Signed-off-by: Kim Phillips <kim.phillips@arm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20170529142754.7fbfb1152fd8f2663de0ea70@arm.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>