dm: core: Add ofnode function to read a 64-bit int

We have a 32-bit version of this function. Add a 64-bit version as well so
we can easily read 64-bit ints from the device tree.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/dm/of_access.h

@@ -218,6 +218,22 @@ struct device_node *of_find_node_by_phandle(phandle handle);
  */
 int of_read_u32(const struct device_node *np, const char *propname, u32 *outp);
 
+/**
+ * of_read_u64() - Find and read a 64-bit integer from a property
+ *
+ * Search for a property in a device node and read a 64-bit value from
+ * it.
+ *
+ * @np:		device node from which the property value is to be read.
+ * @propname:	name of the property to be searched.
+ * @outp:	pointer to return value, modified only if return value is 0.
+ *
+ * @return 0 on success, -EINVAL if the property does not exist,
+ * -ENODATA if property does not have a value, and -EOVERFLOW if the
+ * property data isn't large enough.
+ */
+int of_read_u64(const struct device_node *np, const char *propname, u64 *outp);
+
 /**
  * of_read_u32_array() - Find and read an array of 32 bit integers
  *

include/dm/ofnode.h

@@ -236,6 +236,16 @@ int ofnode_read_u32_default(ofnode ref, const char *propname, u32 def);
  */
 int ofnode_read_s32_default(ofnode node, const char *propname, s32 def);
 
+/**
+ * ofnode_read_u64_default() - Read a 64-bit integer from a property
+ *
+ * @ref:	valid node reference to read property from
+ * @propname:	name of the property to read from
+ * @def:	default value to return if the property has no value
+ * @return property value, or @def if not found
+ */
+int ofnode_read_u64_default(ofnode node, const char *propname, u64 def);
+
 /**
  * ofnode_read_string() - Read a string from a property
  *