perf xyarray: Save max_x, max_y

Save the original array dimensions in xyarrays, so that users can
retrieve them later. Add some inline functions to access these fields.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/20170811232634.30465-1-andi@firstfloor.org


[ As noticed by Jiri, fix up namespacing: xy__method() -> xyarray__method() ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>