EF10 controllers do not have shared memory for communication with the
MC; instead it reads requests and writes responses in host memory,
which allows for longer messages.  It is also responsible for all
datapath control operations and hardware resource allocation, which
requires a large number of new commands and adds more possible error
cases.  MCDI v2 extends the message header to support this.

Update the MCDI protocol definition header to include v2 lengths,
errors and messages, and a few definitions specific to the
SFC9100 family (codenames Farmingdale and Huntington) which is
the first generation of EF10.

Some messages have been extended, so adjust the code accordingly:
- The request for MC_CMD_DRV_ATTACH now includes a datapath firmware
  ID.  This is ignored by Siena but we should fill it in anyway,
  initially always specifying low-latency datapath.
- The response for MC_CMD_GET_LOOPBACK_MODES now includes a 40G
  field.  Accept shorter responses that don't include it.
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>