coresight: Add support for byte counter interrupt feature

The CoreSight block can produce an interrupt on transfer of
programmed number of bytes to ETR-memory. Use this feature
to provide an interface to manage the byte counter value and
to collect a continuous data stream from userspace.

Change-Id: Ic00c9b19483be566d0f05005936b4a6ff7ab52f1
Signed-off-by: Pushkar Joshi <pushkarj@codeaurora.org>