Some, if not most, NKMP PLLs can be set to higher rate that is really
supported by HW.

Implement support for maximum frequency constrain for NKMP PLLs.
Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>