sfc/siena: Rename functions in mcdi headers 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.

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