tmc-etr: Fix the race condition when switch the out_mode

There is race condition which will make usbch be null for usb_qdss_close
when switch the out_mode. Add the lock when enable/disable etr to avoid
the reace condition.

Change-Id: I4c5a28bcb140a9256c717d13ae7578e37ec27cb3
Signed-off-by: Mao Jinlong <jinlmao@codeaurora.org>