sfc/siena: Rename RX/TX functions to avoid conflicts with sfc

For siena use efx_siena_ as the function prefix.
Several functions are not used in Siena, so they are removed.

Use a Siena specific variable name for module parameter
efx_separate_tx_channels.
Move efx_fini_tx_queue() to avoid a forward declaration of
efx_dequeue_buffer().

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