Don't discard AAD and IV output data for AEAD requests.

The T6 can hang when processing certain AEAD requests if the request
sets a flag asking the crypto engine to discard the input IV and AAD
rather than copying them into the output buffer. The existing driver
always discards the IV and AAD as we do not need it. As a workaround,
allocate a single "dummy" buffer when the ccr driver attaches and
change all AEAD requests to write the IV and AAD to this scratch
buffer. The contents of the scratch buffer are never used (similar to
"bogus_page"), and it is ok for multiple in-flight requests to share
this dummy buffer.

Submitted by: Harsh Jain @ Chelsio (original version)
Sponsored by: Chelsio Communications