Squashed 'dts/upstream/' content from commit aaba2d45dc2a

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diff --git a/Bindings/spi/spi-xtensa-xtfpga.txt b/Bindings/spi/spi-xtensa-xtfpga.txt
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+Cadence Xtensa XTFPGA platform SPI controller.
+
+This simple SPI master controller is built into xtfpga bitstreams and is used
+to control daughterboard audio codec.
+
+Required properties:
+- compatible: should be "cdns,xtfpga-spi".
+- reg: physical base address of the controller and length of memory mapped
+  region.