arm64: dts: mediatek: mt6795: Add apmixedsys syscon node

Add the APMIXEDSYS node, providing a syscon to the APMIXED iospace and
also providing PLLs.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20230327083647.22017-3-angelogioacchino.delregno@collabora.com


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>