coresight: tgu: Add snapshot of Trigger Generation Unit

This patch adds a snapshot of TGU driver as of msm-4.9 commit
'a2a8e3e98b6c52fa3c67d0640979d187491f420d' (coresight: tgu: Add
support for Trigger Generation Unit).

Change-Id: I5a7d83a32fd5e67e4a379e73a6f8af7168db18fa
Signed-off-by: Rama Aparna Mallavarapu <aparnam@codeaurora.org>