sfc: Move shared NIC code from falcon.c to new source file nic.c

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

drivers/net/sfc/Makefile

-sfc-y			+= efx.o falcon.o tx.o rx.o falcon_gmac.o \
+sfc-y			+= efx.o nic.o falcon.o tx.o rx.o falcon_gmac.o \
 			   falcon_xmac.o selftest.o ethtool.o qt202x_phy.o \
 			   mdio_10g.o tenxpress.o falcon_boards.o
 sfc-$(CONFIG_SFC_MTD)	+= mtd.o