perf build: Reduce pmu-events related copying and mkdirs

perf build: Reduce pmu-events related copying and mkdirs

When building to an output directory the previous code would remove
files and then copy the source files over.

Each source file copy would have a rule to make its directory. All JSON
for every architecture was considered a source file.

This led to unnecessary copying as a file would be deleted and then the
same file copied again, unnecessary directory making, and copying of
files not used in the build.

A side-effect would be a lot of build messages.

This change makes it so that all computed output files are created and
then compared to all files in the OUTPUT directory.

By filtering out the files that would be copied, unnecessary files can
be determined and then deleted - note, this is a phony target which
would remake the pmu-events.c if always depended upon, and so the
dependency is conditional on there being files to remove.

This has some overhead as the $(OUTPUT)/pmu-events is "find" over rather
than just "rm -fr", but the savings from unnecessary copying, etc.
should make up for this new make overhead.

The copy target just does copying but has a dependency on the directory
it needs being built, avoiding repetitive mkdirs.

The source files for copying only consider the JEVENTS_ARCH unless the
JEVENTS_ARCH is all.

The metric JSON is only generated if appropriate, rather than always
being generated and jevents.py deciding whether or not to use the files.

The mypy and pylint targets are fixed as variable names had changed but
the rules not updated.

The line count of a build with "make -C tools/perf O=/tmp/perf clean all"
prior to this change was 2181 lines, after this change it is 1596
lines.

This is a reduction of 585 lines or about 27%.

The generated pmu-events.c for JEVENTS_ARCH "x86" and "all" were
validated as being identical after this change.

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Leo Yan <leo.yan@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>