dm: add dev_read_u32()

dev_read_u32_default() always returns something even when the property
is missing.  So, it is impossible to do nothing in the case.  One
solution is to use ofnode_read_u32() instead, but adding dev_read_u32()
will be helpful.

BTW, Linux has an equvalent function, device_property_read_u32();
it is clearer that it reads a property.  I cannot understand the
behavior of dev_read_u32() from its name.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

drivers/core/read.c

@@ -10,6 +10,11 @@
 #include <mapmem.h>
 #include <dm/of_access.h>
 
+int dev_read_u32(struct udevice *dev, const char *propname, u32 *outp)
+{
+	return ofnode_read_u32(dev_ofnode(dev), propname, outp);
+}
+
 int dev_read_u32_default(struct udevice *dev, const char *propname, int def)
 {
 	return ofnode_read_u32_default(dev_ofnode(dev), propname, def);