perf cs-etm: Remove duplicate GENMASK() define, use linux/bits.h instead

perf cs-etm: Remove duplicate GENMASK() define, use linux/bits.h instead

Suzuki noticed that this should be more useful in a generic header, and
after looking I noticed we have it already in our copy of
include/linux/bits.h in tools/include, so just use it, test built on
x86-64 and ubuntu 19.04 with:

  perfbuilder@46646c9e848e:/$ aarch64-linux-gnu-gcc --version |& head -1
  aarch64-linux-gnu-gcc (Ubuntu/Linaro 8.3.0-6ubuntu1) 8.3.0
  perfbuilder@46646c9e848e:/$

Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lkml.kernel.org/r/68c1c548-33cd-31e8-100d-7ffad008c7b2@arm.com
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: coresight@lists.linaro.org
Cc: linux-arm-kernel@lists.infradead.org,
Link: https://lkml.kernel.org/n/tip-69pd3mqvxdlh2shddsc7yhyv@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>