UPSTREAM: coresight: etb10: Splitting function etb_enable()

Up until now the relative simplicity of enabling the ETB made it
possible to accommodate processing for both sysFS and perf methods.
But work on claimtags and CPU-wide trace scenarios is adding some
complexity, making the current code messy and hard to maintain.

As such follow what has been done for ETF and ETR components and split
function etb_enable() so that processing for both API can be done
cleanly.

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

(Upstream commit d4989fe88603367e5998af70ee638ae6790d42d1).

Bug: 140266694
Change-Id: Ic4285b48c5d35e78161bd39ace47316888f7743c
Signed-off-by: Yabin Cui <yabinc@google.com>