Just checking "does the chip have an EMAC" doesn't work - there are
targets using those chips which do not have an Ethernet connector and
don't provide the necessary surrounding infrastructure (eg DISCO_F429ZI,
not providing the board emac config call, and HEXIWEAR not providing PHY
info).
Make the targets that actually do want EMAC define their own local
Freescale_EMAC and STM_EMAC labels, and move the drivers into
the corresponding TARGET_ directories, removing the #ifdefs.
Checking DEVICE_EMAC is problematic - particularly for the Odin W2 where
apps have been shutting this off to disable the Wi-fi interface.
Make drivers check a locally-relevant flag instead, pending new
thoughts on how to achieve application/test-relevant flagging for
XXX:get_default_instance() being provided by a system.
However that is achieved, drivers do require a flag set purely by the
target - they mustn't be tripped up by an add-on module providing itself
as the system's default EMAC.