coresight: etm4x: Extract the trace unit controlling

coresight: etm4x: Extract the trace unit controlling

[ Upstream commit 40f682ae5086366d51e29e66eb8a344501245d0d ]

The trace unit is controlled in the ETM hardware enabling and disabling.
The sequential changes for support AUX pause and resume will reuse the
same operations.

Extract the operations in the etm4_{enable|disable}_trace_unit()
functions.  A minor improvement in etm4_enable_trace_unit() is for
returning the timeout error to callers.

Signed-off-by: Leo Yan <leo.yan@arm.com>
Reviewed-by: Mike Leach <mike.leach@linaro.org>
Reviewed-by: James Clark <james.clark@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20250401180708.385396-2-leo.yan@arm.com
Stable-dep-of: 64eb04ae5452 ("coresight: etm4x: Add context synchronization before enabling trace")
Signed-off-by: Sasha Levin <sashal@kernel.org>