sfc: Move more Falcon-specific code and definitions into falcon.c

In particular, fold in the whole of falcon_xmac.c.

Drop some entirely unused definitions.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

diff --cc drivers/net/ethernet/sfc/Makefile
Simple merge

diff --cc drivers/net/ethernet/sfc/falcon.c
Simple merge

diff --cc drivers/net/ethernet/sfc/falcon_xmac.c
Simple merge

diff --cc drivers/net/ethernet/sfc/nic.h
Simple merge

diff --cc drivers/net/ethernet/sfc/regs.h
Simple merge