bif: bif-core: add BIF NVM object writing support

Add a function to the bif-core driver which provides a means to
write new BIF data objects into the non-volatile memory (NVM)
of a BIF slave.  Also add functions which can be used to
overwrite or delete an existing BIF object.

Change-Id: I6cd48409c696bd60a4d52b0fac8782c58d744df1
Signed-off-by: David Collins <collinsd@codeaurora.org>