clk: meson8b: clean up pll clocks

clk: meson8b: clean up pll clocks

Remove the pll registration function and helpers. Replace unnecessary
configuration struct with static initialization of the desired clock
type.

Tested-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>