diag: Set Diag mode correctly when USB is disconnected

Diag driver sets the mode on the peripherals to Non real time mode
when USB is disconnected. This should happen only when there are
DCI clients and/or On Device Logging process are active. The mode
should be real time otherwise. This patch adds logic to set the
mode to realtime when there are no active processes.

Change-Id: I3a7c08d5a74acecbe4150913c5e8cca6a599edf5
Signed-off-by: Ravi Aravamudhan <aravamud@codeaurora.org>