bif: bif-core: add auto task triggering support

Add support in the bif-core driver for enabling and disabling
automatic task triggering for specified tasks.  One example of
auto task triggering is the periodic polling method employed by
the BIF slave temperature function to check for high or low
temperature conditions.

Change-Id: If01071debd430c084be344549ecf2e8b281d4e05
Signed-off-by: David Collins <collinsd@codeaurora.org>