coresight: tmc: leverage etr disable/enable when switching mode

Disable ETR first and enable it again with new mode to switch
out_mode. In this way, we can leverage etr_disable and etr_enable
function and avoid doing same thing.

Change-Id: I76f8e34b1ca449bf18610e000a09fb6d3d5803bf
Signed-off-by: Tingwei Zhang <tingwei@codeaurora.org>