dm: tpm: sandbox: Convert TPM driver to driver model

Convert the sandbox TPM driver to use driver model. Add it to the device
tree so that it can be found on start-up.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Christophe Ricard <christophe-h.ricard@st.com>
Reviewed-by: Heiko Schocher <hs@denx.de>
diff --git a/arch/sandbox/dts/sandbox.dts b/arch/sandbox/dts/sandbox.dts
index 8927527..758c4a5 100644
--- a/arch/sandbox/dts/sandbox.dts
+++ b/arch/sandbox/dts/sandbox.dts
@@ -156,6 +156,10 @@
 		sides = <4>;
 	};
 
+	tpm {
+		compatible = "google,sandbox-tpm";
+	};
+
 	triangle {
 		compatible = "demo-shape";
 		colour = "cyan";