coresight: add remote etm driver support in upstream implementation

Add remote etm driver in upstream implementation of Coresight
driver.
This change copies coresight-remote-etm.c file from
drivers/coresight (commit : 53d1dd96)
to driver/hwtracing/coresight directory.

Change-Id: I77a1aaf10aaf3f3010ab19d5878bb53dcc504c29
Signed-off-by: Shashank Mittal <mittals@codeaurora.org>