clk: mediatek: clk-mt8192: Add clock mux notifier for mfg_pll_sel

Following the changes that were done for mt8183, add a clock notifier
for the GPU PLL selector mux: this allows safe clock rate changes by
temporarily reparenting the GPU to a safe clock (clk26m) while the
MFGPLL is reprogrammed and stabilizes.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Link: https://lore.kernel.org/r/20220927101128.44758-11-angelogioacchino.delregno@collabora.com


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