drm/mgag200: Store values (not bits) in struct mgag200_pll_values

The fields in struct mgag200_pll_values currently hold the bits of
each register. Store the PLL values instead and let the PLL-update
code figure out the bits for each register.

Until now, the compute function either stored plain values or register
bits in struct mgag200_pll_values. The rsp update function used the
values as-is. This made it very hard to correctly interpret the stored
values (e.g., for logging or debugging). With the cleanup, the stored
values now have a clear meaning.

v2:
	* add a bit more context in the commit message (Sam)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210714142240.21979-7-tzimmermann@suse.de