sfc/siena: Remove build references to missing functionality

Functionality not supported or needed on Siena includes:
- Anything for EF100
- EF10 specifics such as register access, PIO and TSO offload.
Also only bind to Siena NICs.

Remove EF10 specifics from nic.h.
The functions that start with efx_farch_ will be removed from sfc.ko
with a subsequent patch.
Add the efx_ prefix to siena_prepare_flush() to make it consistent
with the other APIs.

Signed-off-by: Martin Habets <habetsm.xilinx@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>