ARM: imx_v7_defconfig: remove board specific part from environment ...

This makes no sense for a generic defconfig.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

ARM: Add a imx_v7_defconfig ...

This is a nearly full-blown config for the v7 i.MX (i.MX51, i.MX53 and
i.MX6).

currently the following images are built:

 barebox-imx51-babbage.img
 barebox-imx53-loco.img
 barebox-imx6-realq7.img
 barebox-genesi-efikasb.img

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>