clk: mediatek: mt2712: Move apmixedsys clock driver to its own file

The only clock driver that does not support mtk_clk_simple_probe() is
apmixedsys: in preparation for enabling module build of non-critical
mt2712 clocks, move this to its own file.
While at it, also fix some indentation issues in the PLLs table.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Link: https://lore.kernel.org/r/20230306140543.1813621-9-angelogioacchino.delregno@collabora.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>