dm: Add Hardware Spinlock class

This is uclass for Hardware Spinlocks.
It implements two mandatory operations: lock and unlock
and one optional relax operation.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
diff --git a/arch/sandbox/dts/test.dts b/arch/sandbox/dts/test.dts
index 6722e18..12d39d8 100644
--- a/arch/sandbox/dts/test.dts
+++ b/arch/sandbox/dts/test.dts
@@ -742,6 +742,10 @@
 	pinctrl {
 		compatible = "sandbox,pinctrl";
 	};
+
+	hwspinlock@0 {
+		compatible = "sandbox,hwspinlock";
+	};
 };
 
 #include "sandbox_pmic.dtsi"