perf vendor events: Add support for pmu events vendor subdirectory

For some architectures (like arm), it is required to support a vendor
subdirectory and not locate all the JSONs for a specific vendor in the
same folder.

This is because all the events for the same vendor will be placed in the
same pmu events table, which may cause conflict.  This conflict would be
in the instance that a vendor's custom implemented events do have the
same meaning on different platforms, so events in the pmu table would
conflict. In addition, per list command may show events which are not
even supported for a given platform.

This patch adds support for a arch/vendor/platform directory hierarchy,
while maintaining backwards-compatibility for existing arch/platform
structure. In this, each platform would always have its own pmu events
table.

In generated file pmu_events.c, each platform table name is in the
format pme{_vendor}_platform, like this:

struct pmu_events_map pmu_events_map[] = {
{
	.cpuid = "0x00000000420f5160",
	.version = "v1",
	.type = "core",
	.table = pme_cavium_thunderx2
},
{
	.cpuid = 0,
	.version = 0,
	.type = 0,
	.table = 0,
},
};

Signed-off-by: John Garry <john.garry@huawei.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
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: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.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/1520506716-197429-5-git-send-email-john.garry@huawei.com
Link: http://lkml.kernel.org/r/1521047452-28565-1-git-send-email-john.garry@huawei.com
[ Add missing limits.h include, fixing the build on at least all Alpine Linux versions tested (3.4 to 3.7 + edge), ]
[ Applied a patch to fix reading ./.. directories in XFS, see second Link tag ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>