coresight: add support for byte counter for scatter gather feature

Byte counter interrupt feature provides an interface to set byte counter
value and collect continuous trace data stream from userspace. Add support
to read this trace data stream when scatter gather feature is enabled for
TMC ETR configuration.

Change-Id: Ic755b7ae14b4bf13f7f28897ec8827476366eaf7
Signed-off-by: Sarangdhar Joshi <spjoshi@codeaurora.org>