dt-bindings: tpm: document properties for cr50

Add TPM2.0 PTP FIFO compatible SPI interface for chips with Cr50
firmware.

Cc: Andrey Pronin <[e-mail]>
Cc: Duncan Laurie <[e-mail]>
Cc: Jason Gunthorpe <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Guenter Roeck <[e-mail]>
Cc: Alexander Steffen <[e-mail]>
Cc: Heiko Stuebner <[e-mail]>
Signed-off-by: Andrey Pronin <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Signed-off-by: Stephen Boyd <[e-mail]>
Acked-by: Jarkko Sakkinen <[e-mail]>
Signed-off-by: Jarkko Sakkinen <[e-mail]>

Documentation/devicetree/bindings/security/tpm/google,cr50.txt

···
+* H1 Secure Microcontroller with Cr50 Firmware on SPI Bus.
+
+H1 Secure Microcontroller running Cr50 firmware provides several
+functions, including TPM-like functionality. It communicates over
+SPI using the FIFO protocol described in the PTP Spec, section 6.
+
+Required properties:
+- compatible: Should be "google,cr50".
+- spi-max-frequency: Maximum SPI frequency.
+
+Example:
+
+&spi0 {
+	tpm@0 {
+		compatible = "google,cr50";
+		reg = <0>;
+		spi-max-frequency = <800000>;
+	};
+};