Add fdtget utility to read property values from a device tree

This simply utility makes it easy for scripts to read values from the device
tree. It is written in C and uses the same libfdt as the rest of the dtc
package.

What is it for:
- Reading fdt values from scripts
- Extracting fdt information within build systems
- Looking at particular values without having to dump the entire tree

To use it, specify the fdt binary file on command line followed by a list of
node, property pairs. The utility then looks up each node, finds the property
and displays the value.

Each value is printed on a new line.

fdtget tries to guess the type of each property based on its contents. This
is not always reliable, so you can use the -t option to force fdtget to decode
the value as a string, or byte, etc.

To read from stdin, use - as the file.

Usage:
	fdtget <options> <dt file> [<node> <property>]...
Options:
	-t <type>	Type of data
	-h		Print this help

<type>	s=string, i=int, u=unsigned, x=hex
	Optional modifier prefix:
		hh or b=byte, h=2 byte, l=4 byte (default)

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

util.h

@@ -140,4 +140,14 @@ int utilfdt_write_err(const char *filename, const void *blob);
  */
 int utilfdt_decode_type(const char *fmt, int *type, int *size);
 
+/*
+ * This is a usage message fragment for the -t option. It is the format
+ * supported by utilfdt_decode_type.
+ */
+
+#define USAGE_TYPE_MSG \
+	"<type>\ts=string, i=int, u=unsigned, x=hex\n" \
+	"\tOptional modifier prefix:\n" \
+	"\t\thh or b=byte, h=2 byte, l=4 byte (default)\n";
+
 #endif /* _UTIL_H */