arm64: dts: qcom: move common parts for sa8775p-ride variants into a .dtsi

In order to support multiple revisions of the sa8775p-ride board, create
a .dtsi containing the common parts and split out the ethernet bits into
the actual board file as they will change in revision 3.
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Link: https://lore.kernel.org/r/20240627114212.25400-3-brgl@bgdev.plSigned-off-by: Bjorn Andersson <andersson@kernel.org>