Update binding documentation

use simple-bus for parent node
add size cell for register size
use reg_vddd to demonstrate supply relation
Remove all current limit stuff
Remove unused defines and variable
Refactor mxs_set_voltage
Remove supply names since they are in DT binding
Reorder regulators
Add regulator vddmem
Add module alias
Refactor regulator ops
Add more error messages
Change driver name
Refactor white listing of regulator description