perf cs-etm: Refactor out ETMv4 header saving

mainline inclusion
from mainline-v5.14-rc4
commit c9ccc96b
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I636PS
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c9ccc96bf6f28d83ef497ee985b8f6ffd493de2a



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Extract a function for saving the ETMv4 header because this will be used
for ETE in a later commit.

Reviewed-by: Leo Yan <leo.yan@linaro.org>
Signed-off-by: James Clark <james.clark@arm.com>
Acked-by: Suzuki Poulouse <suzuki.poulose@arm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: John Garry <john.garry@huawei.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: coresight@lists.linaro.org
Cc: linux-arm-kernel@lists.infradead.org
Link: https //lore.kernel.org/r/20210806134109.1182235-4-james.clark@arm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Junhao He <hejunhao3@huawei.com>