coresight: Refactor etm4_config_timestamp_event()

coresight: Refactor etm4_config_timestamp_event()

Remove some of the magic numbers and try to clarify some of the
documentation so it's clearer how this sets up the timestamp interval.

Return errors directly instead of jumping to out and returning ret,
nothing needs to be cleaned up at the end and it only obscures the flow
and return value.

Add utilities for programming resource selectors that do compile time
checks for constants or WARN_ONs for non-constant values. FIELD_PREP
includes compile time checks so we only need to add an additional
BUILD_BUG_ON for resource == 0 in pair mode.

Tested-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: James Clark <james.clark@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20251128-james-cs-syncfreq-v8-3-4d319764cc58@linaro.org