aw_rtc: Register the clocks

Since latest DTS update the rtc is supposed to register two clocks :

• osc32k (the 32k oscillator on the board that the RTC uses directly and

that other peripheral can use)

• iosc (the internal oscillator of the RTC when available which frequency

depend on the SoC revision)

Since we need the RTC before the proper clock control unit (because it uses
those clocks) attach it a BUS_PASS_BUS + MIDDLE and attach the clock control
unit at BUS_PASS_BUS + LAST for the SoC that requires it.

Tested On: A20, H3, A64

MFC after: 1 month