dt-bindings: mfd: syscon: Add mt7988-topmisc

Add compatible for Mediatek mt7988 topmisc syscon.
This hardware block contains 2 functional blocks

- a powercontroller which is not needed (switched by atf)
- a multiplexer for high-speed Combo-Phy

This compatible is only for the multiplexer part.

Signed-off-by: Frank Wunderlich <frank-w@public-files.de>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20250422132438.15735-6-linux@fw-web.de


Signed-off-by: Lee Jones <lee@kernel.org>