arm64: dts: qcom: sm8450-nagara: Separate out Nagara platform dtsi

Turns out 1 IV is not the only Nagara device, reflect that in the DTS.

Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221114095654.34561-2-konrad.dybcio@linaro.org