ipmi: Make ipmi_demangle_device_id more generic

Currently, ipmi_demagle_device_id requires a full response buffer in its
data argument. This means we can't use it to parse a response in a
struct ipmi_recv_msg, which has the netfn and cmd as separate bytes.

This change alters the definition and users of ipmi_demangle_device_id
to use a split netfn, cmd and data buffer, so it can be used with
non-sequential responses.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>

Fixed the ipmi_ssif.c and ipmi_si_intf.c changes to use data from the
response, not the data from the message, when passing info to the
ipmi_demangle_device_id() function.

Signed-off-by: Corey Minyard <cminyard@mvista.com>