coresight: reset "enable_sink" flag when need be

When using coresight from the perf interface sinks are specified
as part of the perf command line.  As such the sink needs to be
disabled once it has been acknowledged by the coresight framework.
Otherwise the sink stays enabled, which may interfere with other
sessions.

This patch removes the sink selection check from the build path
process and make it a function on it's own.  The function is
then used when operating from sysFS or perf to determine what
sink has been selected.

If operated from perf the status of the "enable_sink" flag is
reset so that concurrent session can use a different sink.  When
used from sysFS the status of the flag is left untouched since
users have full control.

The implementation doesn't handle a scenario where a sink has
been enabled from sysFS and another sink is selected from the
perf command line as both modes of operation are mutually
exclusive.

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>