clk: mediatek: mt7986-apmixed: Use PLL_AO flag to set critical clock

clk: mediatek: mt7986-apmixed: Use PLL_AO flag to set critical clock

Instead of calling clk_prepare_enable() at probe time, add the PLL_AO
flag to CLK_APMIXED_ARMPLL clock: this will set CLK_IS_CRITICAL.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Tested-by: Daniel Golle <daniel@makrotopia.org>
Link: https://lore.kernel.org/r/20230306140543.1813621-33-angelogioacchino.delregno@collabora.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>