mxs: Implement common function to setup VDDx

mxs: Implement common function to setup VDDx

Implement common function to setup the VDDIO, VDDD and VDDA voltage.
Right now, there are two almost identical functions to setup VDDIO
and VDDD, which is prone to breakage. Pull out the differences into
constant structure and pass them as an argument to the common function.

Moreover, the function has almost identical loops for setting higher
and lower VDDx voltage. Merge these two loops.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>