sfc: Rename efx_board::init_leds to init_phy and use for SFN4111T

efx_board::init_leds was introduced as a second stage of
initialisation because of the inter-dependency between the board and
PHY.  We want to move board initialisation into NIC probing, which is
too early to use MDIO, so SFN4111T initialisation also needs to be
split.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>