dt-bindings: arm: qcom: Add Lenovo ThinkPad T14s Gen 6

Document the X1E78100-based ThinkPad.

X1E78100 is a binned version of X1E80100, hence use the latter's
compatible string as fallback.

Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240828-topic-t14s_upstream-v2-1-49faea18de84@quicinc.com


Signed-off-by: Bjorn Andersson <andersson@kernel.org>