arm64: dts: qcom: x1e78100-lenovo-thinkpad-t14s: Enable IRIS

arm64: dts: qcom: x1e78100-lenovo-thinkpad-t14s: Enable IRIS

IRIS firmware for the Lenovo ThinkPad T14s is already upstream in
linux-firmware at qcom/x1e80100/LENOVO/21N1/qcvss8380.mbn, so enable IRIS
for the T14s with the corresponding firmware-name property.

Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on Thinkpad T14S OLED
Signed-off-by: Stephan Gerhold <stephan.gerhold@linaro.org>
Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Link: https://lore.kernel.org/r/20250915-x1e-iris-dt-v2-5-1f928de08fd4@linaro.org
Signed-off-by: Bjorn Andersson <andersson@kernel.org>