board/t208xrdb: VID support

The fuse status register provides the values from on-chip
voltage ID efuses programmed at the factory.
These values define the voltage requirements for
the chip. u-boot reads FUSESR and translates the values
into the appropriate commands to set the voltage output
value of an external voltage regulator.

Signed-off-by: Ying Zhang <b40530@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>