dt-bindings: msm: dsi-phy-14nm: Document SM6125 variant

dt-bindings: msm: dsi-phy-14nm: Document SM6125 variant

Document availability of the 14nm DSI PHY on SM6125.  Note that this
compatible uses the SoC-suffix variant, intead of postfixing an
arbitrary number without the sm/sdm portion.  The PHY is not powered by
a vcca regulator like on most SoCs, but by the MX power domain that is
provided via the power-domains property and a single corresponding
required-opps.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Marijn Suijten <marijn.suijten@somainline.org>
Patchwork: https://patchwork.freedesktop.org/patch/548979/
Link: https://lore.kernel.org/r/20230723-sm6125-dpu-v4-12-a3f287dd6c07@somainline.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>