drm/nouveau/pll/gk104: fix PLL instability due to bad configuration with gddr5

This patch uses an approach closer to the nvidia driver to configure
both PLLs for high gddr5 memory clocks (usually above 2400MHz)

Previously nouveau used the one PLL as it was used for the lower clocks
and just adjusted the second PLL to get as close as possible to the
requested clock.  This means for my card, that I got a 4050 MHz clock
although 4008 MHz was requested.

Now the driver iterates over a list of PLL configuration also used by
the nvidia driver and then adjust the second PLL to get near the
requested clock.  Also it hold to some restriction I found while
analyzing the PLL configurations

This won't fix all gddr5 high clock issues itself, but it should be
fine on hybrid gpu systems as found on many laptops these days.  Also
switching while normal desktop usage should be a lot more stable than
before.

v2: move the pll code into ramgk104

Signed-off-by: Karol Herbst <nouveau@karolherbst.de>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>