Add minor updates to README.fdt-control

A few things have changed since this doc was written, so update it to
match the current state of things.

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

doc/README.fdt-control

@@ -49,6 +49,12 @@ the features of each board in the device tree file, and have a single
 generic source base.
 
 To enable this feature, add CONFIG_OF_CONTROL to your board config file.
+It is currently supported on ARM, x86 and Microblaze - other architectures
+will need to add code to their arch/xxx/lib/board.c file to locate the
+FDT. Alternatively you can enable generic board support on your board
+(with CONFIG_SYS_GENERIC_BOARD) if this is available (as it is for
+PowerPC). For ARM, Tegra and Exynos5 have device trees available for
+common devices.
 
 
 What is a Flat Device Tree?
@@ -99,7 +105,8 @@ Then run the compiler (your version will vary):
 	*   Bad configuration:	0
 	* Strange test result:	0
 
-You will also find a useful ftdump utility for decoding a binary file.
+You will also find a useful fdtdump utility for decoding a binary file, as
+well as fdtget/fdtput for reading and writing properties in a binary file.
 
 
 Where do I get an fdt file for my board?