coresight: tmc: Correct the status for ETR disable

Mode in etr drvdata is not reset to CS_MODE_DISABLED in USB case.
In this case, following ETR enablement on mem mode won't work.  Set
the mode status correctly.  Coresight source should be disabled
in reset case and echo 0 > enable_source case.  Decrease the refcnt
to disable the source correctly.

Change-Id: I6f88efcd22ef56dc12f85a821a1dc004b4dda3d8
Signed-off-by: Tingwei Zhang <tingwei@codeaurora.org>