perf vendor events: Drop support for unused topic directories

Currently a topic subdirectory is supported in the pmu-events dir, in
the following sample structure: /arch/platform/subtopic/mysubtopic.json

Upto 256 levels of topic subdirectories are supported. So this means
that JSONs may be located in a topic dir as well as the platform dir.

This topic subdirectory causes problems if we want to add support for a
vendor dir in the pmu-events structure (in the form
arch/platform/vendor), in that we cannot differentiate between a vendor
dir and a topic dir.

Since the topic dir feature is not used, drop it so it does not block
adding vendor subdirectory support.

Signed-off-by: John Garry <john.garry@huawei.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ganapatrao Kulkarni <ganapatrao.kulkarni@cavium.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Shaokun Zhang <zhangshaokun@hisilicon.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: William Cohen <wcohen@redhat.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linuxarm@huawei.com
Link: http://lkml.kernel.org/r/1520506716-197429-4-git-send-email-john.garry@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>