clk: mediatek: mt8195: use ext_clock_rates

clk: mediatek: mt8195: use ext_clock_rates

Convert the mt8195 clock driver to use ext_clock_rates.

Now that we have the ext_clock_rates feature and also mux clock parents
have been converted to struct mtk_parent, we can remove the hack of
adding "missing" topckgen clocks. Instead we can use the proper parents.

The topckgen ID map is still needed though because the upstream
dt-bindings didn't use the conventional number ordering by clock type
for these.

Reviewed-by: Julien Stephan <jstephan@baylibre.com>
Link: https://patch.msgid.link/20260309-clk-mtk-mt8188-drop-extra-top-clocks-v1-2-6ee4743a8465@baylibre.com
Signed-off-by: David Lechner <dlechner@baylibre.com>