[rt305x] Add initial RT5350 and MT7620 glue.

• Add in chipset awareness to the obio bus layout (ie, which devices are where);
• Add in some USB OTG changes to be aware of the newer stuff;
• Add in a configurable primary console - some chips use the normal UART, some use UARTLITE.

Tested (by Stanislav);

• RT3050 (NFS)
• RT5350 (NFS, MFS)
• MT7620 (USB)

Submitted by: Stanislav Galabov <sgalabov@gmail.com>