As it stood, the mediatek cpufreq driver could get away with never
really having a private driver instance struct. This is because all data
was stored in the per-domain structs.
However, this complicates matters when actual per-instance data like the
variant struct is introduced. Instead of having a pointer to it for
every domain, have a pointer to a global "priv" struct that can be
extended over time, and rename the "data" struct to "domain" to
distinguish its purpose better.
Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@xxxxxxxxxxxxx>