msm: clock-8610: add clock entry for Debug and ETM registers save-restore

When there is a power collapse the Debug and ETM registers of
MSM8610 need to be saved and subsequently restored using memory
mapped accesses. Add the support for clocks in preparation of
enabling this feature.

Change-Id: Ifd405ea2953df0fc407c3ffa4593b5fb376e5c7c
Signed-off-by: Aparna Das <adas@codeaurora.org>