Multiple fixes for rockchip iodomain driver:

Multiple fixes for rockchip iodomain driver:
- always initialize selector of voltage signaling standard.
  Various versions of U-boot leaves voltage signaling standard settings
  for PMUIO2 domain in different state.  Always initialize it
  into expected state.
- start the driver as early as possible, the IO domains should be
  initialized before other drivers are attached.
- rename RK3399 register to its name founds in TRM.

This is the second part of fixes for serial port corruption observed after
DT 5.6 import.

Reviewed by:	manu
MFC after:	1 week