perf mem: Search event name with more flexible path

The perf tool searches a memory event name under the folder
'/sys/devices/cpu/events/', this leads to the limitation for the
selection of a memory profiling event which must be under this folder.

Thus it's impossible to use any other event as memory event which is not
under this specific folder, e.g. Arm SPE hardware event is not located
in '/sys/devices/cpu/events/' so it cannot be enabled for memory
profiling.

This patch changes to search folder from '/sys/devices/cpu/events/' to
'/sys/devices', so it give flexibility to find events which can be used
for memory profiling.

Signed-off-by: Leo Yan <leo.yan@linaro.org>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Link: https://lore.kernel.org/r/20201106094853.21082-2-leo.yan@linaro.org


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