board/BuR: provide real clock-frequency instead a divider

board/BuR: provide real clock-frequency instead a divider

Actual am335x-fb implementation takes now a real clock frequency instead
a divider. So this component doesn't need to know anymore some base
frequency of the LCDC, we simply provide the pixel-clock frequency.

Signed-off-by: Hannes Schmelzer <[email protected]>
Reviewed-by: Anatolij Gustschin <[email protected]>