Adjust node naming to match requirements from dt-schema.
Also add only and default required PHY name "dsi" to the node.

Fixes warnings generated by `make qcom-apq8064-asus-nexus7-flo.dtb`:
arch/arm/boot/dts/qcom-apq8064-sony-xperia-yuga.dt.yaml: mdss_dsi@4700000: $nodename:0: 'mdss_dsi@4700000' does not match '^dsi(@.*)?$'
	From schema: Documentation/devicetree/bindings/display/msm/dsi-controller-main.yaml
Signed-off-by: NDavid Heidelberg <david@ixit.cz>
Signed-off-by: NBjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20211225131357.13751-1-david@ixit.cz