sfc: Use a single blink implementation

Only some PHYs have firmware support for a LED blink mode, so we
currently blink the others in a timer function.  Since all PHYs have
simple on and off modes, we don't gain anything by using multiple
blink implementations.  Also, since we have a process context there
is no need to use a timer.

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