[PATCH] drm/radeon/kms/atom: add support for spread spectrum (v2)

[Alex D. <ale...@gm...>]

Spread spectrum is a periodic disturbance added to the feedback
divider to change the pixel clock periodically to reduce interference.
Used for LVDS.

I don't have an atom-based laptop at the moment, so it's only been
tested on desktop cards.  I'd appreciate feedback from laptop users.

Alex