dt-bindings: soc: mediatek: convert pwrap documentation

- Convert soc/mediatek/pwrap.txt to soc/mediatek/mediatek,pwrap.yaml
- Add syscon compatible const for mt8186 and mt8195 to match the DTS needs,
  which is missing from pwrap.txt.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Alexandre Mergnat <amergnat@baylibre.com>
Link: https://lore.kernel.org/r/20221005-mt6357-support-v8-2-560caaafee53@baylibre.com


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