greybus: allocate gbufs using the connection

greybus: allocate gbufs using the connection

Switch to using the connection rather than the host device as
the locus for doing Greybus buffer allocation.  A connection
encapsulates both the host device (whose driver is what's required
for allocation) and the *destination* cport id.  Record the
connection a gbuf is associated with rather than the host module and
(unspecified) cport id.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>