coresight: add support to enable remote processor etm tracing on boot

Add support to allow enabling remote processor etm tracing on boot by
default so users don't have to enable it explicitly from sysfs.

Change-Id: I7f719d0b5a504a35cba503c60a7d5d9f8434b309
Signed-off-by: Aparna Das <adas@codeaurora.org>