UPSTREAM: coresight: tmc-etr: Fix updating buffer in not-snapshot mode.

TMC etr always copies all available data to perf aux buffer, which
may exceed the available space in perf aux buffer. It isn't suitable
for not-snapshot mode, because:
1) It may overwrite previously written data.
2) It may make the perf_event_mmap_page->aux_head report having more
or less data than the reality.

So change to only copy the latest data fitting the available space in
perf aux buffer.

Signed-off-by: Yabin Cui <yabinc@google.com>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20190829202842.580-14-mathieu.poirier@linaro.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

(Upstream commit 13af88f312fc57becacfcbb1cc77f844281a30ec).

Bug: 140266694
Change-Id: I17bbfd65d1e89e307298cf8e7d59d2062afeedae
Signed-off-by: Yabin Cui <yabinc@google.com>