esoc: Add debug engine for external modems.

Modifies the behavior of the command engine
to mask out certain commands/notifications sent to the
external mdm, for the purposes of debugging the external
mdm.

Change-Id: Iff35fd87f6d66849f6ec7d2924e1547400967c4e
Signed-off-by: Hanumant Singh <hanumant@codeaurora.org>
Signed-off-by: Bruce Levy <blevy@codeaurora.org>