drivers/net/: get mac address from environment

The environment is the canonical storage location of the mac address, so
we're killing off the global data location and moving everything to
querying the env directly.

The drivers that get converted here:
	3c589
	4xx_enet
	dc2114x
	dm9000x
	enc28j60
	fsl_mcdmafec
	ks8695eth
	mcffec
	rtl8019
	rtl8169
	s3c4510b_eth
	xilinx_emac
	xilinx_emaclite

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
CC: Ben Warren <biggerbadderben@gmail.com>
CC: Rolf Offermanns <rof@sysgo.de>
CC: Stefan Roese <sr@denx.de>
CC: Sascha Hauer <saschahauer@web.de>
CC: TsiChung Liew <Tsi-Chung.Liew@freescale.com>
CC: Greg Ungerer <greg.ungerer@opengear.com>
CC: Xue Ligong <lgxue@hotmail.com>
CC: Masami Komiya <mkomiya@sonare.it>
CC: Curt Brune <curt@cucy.com>
CC: Michal SIMEK <monstr@monstr.eu>