coresight: etm4x: Refactor probing routine

coresight: etm4x: Refactor probing routine

CoreSight ETM with system register access may not have a
memory mapped i/o access. Refactor the ETM specific probing
into a common routine to allow reusing the code for such ETMs.

Link: https://lore.kernel.org/r/20210110224850.1880240-24-suzuki.poulose@arm.com
Cc: Mike Leach <mike.leach@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20210201181351.1475223-26-mathieu.poirier@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>