arm64: dts: mediatek: mt8195: Fix systimer 13 MHz clock description

arm64: dts: mediatek: mt8195: Fix systimer 13 MHz clock description

The systimer block derives its 13 MHz clock by dividing the main 26 MHz
oscillator clock by 2 internally, not through the TOPCKGEN clock
controller.

On the MT8195 this divider is set either by power-on-reset or by the
bootloader. The bootloader may then make the divider unconfigurable to,
but can be read out by, the operating system.

Making the systimer block take the 26 MHz clock directly requires
changing the implementations. As an ABI compatible fix, change the
input clock of the systimer block a fixed factor divide-by-2 clock
that takes the 26 MHz oscillator as its input.

Fixes: 37f2582883be ("arm64: dts: Add mediatek SoC mt8195 and evaluation board")
Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20221201084229.3464449-4-wenst@chromium.org
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>