[Nouveau] PWM-based voltage management input clock

[Martin Peres]

Hello,

We recently reverse engineered PWM-based voltage management but found an 
odity in the input clock frequency for the PWM controller. It seems like 
RM is assuming an input clock of 27.648 MHz instead of the actual 27MHz 
crystal found on the board.

I thus have the following questions:
  - Is it a fixed value hardcoded in RM? (Current way it is done in Nouveau)
  - Should we use crystal_MHz * 1.024?

I could spend some time hooking up my osciloscope to the VR to check if 
it is a bringup issue but it would not help Nouveau much as we need to 
reproduce the behaviour of RM anyway since this is the only validated 
configuration.

Thanks in advance,
Martin

PS: The registers for this PWM controller are 0x20340 and 0x20344.