perf: disable PARALLEL_MAKE

perf: disable PARALLEL_MAKE

Autobuilder builds periodically and now more frequently have been
failing because of a race between the perf build and the newly
separated libtraceevent - perf tries to link libtraceevent.a, which
hasn't finished building yet in those cases.

This disables the parallel build to prevent that.

(From OE-Core rev: cd1e98513016c01e32bdb175ec7225d7378d952c)

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>