clk: mediatek: mt8186-topckgen: Add GPU clock mux notifier

Following the changes done to MT8183, MT8192, MT8195, register a
clock notifier for MT8186, allowing safe clockrate updates for the
MFG PLL.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Link: https://lore.kernel.org/r/20221024102307.33722-11-angelogioacchino.delregno@collabora.com


Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>