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/include/asm/state.h b/arch/sandbox/include/asm/state.h
index 5a14485..c724827 100644
--- a/arch/sandbox/include/asm/state.h
+++ b/arch/sandbox/include/asm/state.h
@@ -101,6 +101,7 @@
 
 	ulong next_tag;			/* Next address tag to allocate */
 	struct list_head mapmem_head;	/* struct sandbox_mapmem_entry */
+	bool hwspinlock;		/* Hardware Spinlock status */
 };
 
 /* Minimum space we guarantee in the state FDT when calling read/write*/