coresight: set appropriate clock rate for coresight devices

For certain coresight devices probed via amba framework the clock
rate is not being set during probe time. The patch sets the rate
to an appropriate value instead of relying on default behavior.

Change-Id: I15607dcb06564a603910709fafb9eba563bf102c
Signed-off-by: Satyajit Desai <sadesai@codeaurora.org>