vf610twr: Add default environment in line with other Freescale boards

This adds a default environment which should be able to support 3.0.15
Timesys and 3.11 kernels.

Series-changes: 3
- add dt boot support
- use ttyLP1 as console
- change loadaddr and sys text as iMX6SL
- NOTE: It needs to be boot tested as I don't have the board

Series-changes: 2
- fix console for ttymxc1 (Fabio)

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
vf610twr: Remove SoC name from U-Boot prompt

We've been dropping SoC name from U-Boot prompt as it increase
complexity for automatic testing and makes line longer for no good
reason.

Series-to: u-boot
Series-version: 3

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>