msm: qdss: make qdss_clk_enable/disable external functions

Move qdss_clk_enable/disable declarations to the external qdss header file.
Add reference counting and mutex locking to make them useable by clients.

Change-Id: If8a5bd9783138af1f9d620e78ecbd0163ff25a6b
Signed-off-by: Pratik Patel <pratikp@codeaurora.org>