coresight: add support to enable multiple coresight paths

Current coresight implementation supports enabling of a
single path. This patch adds support to enable multiple source
to sink paths. We build a path from source to sink when any
source is enabled and store it in a list. When the source is
disabled, we fetch the corresponding path from the list and
decrement the refcount on each device in the path. The device
is disabled if the refcount reaches zero.

Change-Id: Idd3dcfd0346bdfd39f41ac13e8e53068907c14e4
Signed-off-by: Satyajit Desai <sadesai@codeaurora.org>