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