sfc/siena: Rename functions in efx headers to avoid conflicts with sfc

When building with allyesconfig there are many identical
symbol names.
For siena use efx_siena_ as the function and variable prefix
to avoid build errors.

efx_mtd_remove_partition can become static as it is no longer called
from other files.
efx_ticks_to_usecs and efx_xmit_done_single are not used in Siena, so
they are removed.
Several functions are only used inside efx_channels.c for Siena so
they can become static.

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