drm/mgag200: Move hiprilvl setting into separate functions

The hiprivlvl settings are now updated in mgag200_g200se_set_hiprilvl()
and mgag200_g200ev_set_hiprilvl().

v2:
	* replace uint8_t with u8

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Tested-by: John Donnelly <John.p.donnelly@oracle.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Emil Velikov <emil.velikov@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200515083233.32036-11-tzimmermann@suse.de