smsc911x: Unconditionally include linux/smscphy.h in smsc911x.h

The energy detect enable/disable code in the driver uses some
register defines in this header unconditionally, so guarding
the smscphy.h header include with CONFIG_SMSC_PHY leads to
build failures in some configurations.

Reported-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>