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>