Convert CONFIG_CMD_DIAG to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_DIAG

Signed-off-by: Simon Glass <sjg@chromium.org>
[trini: imply CMD_DIAG on some keymile configs]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/arch/arm/mach-kirkwood/Kconfig b/arch/arm/mach-kirkwood/Kconfig
index 4a7e36e..2dd107a 100644
--- a/arch/arm/mach-kirkwood/Kconfig
+++ b/arch/arm/mach-kirkwood/Kconfig
@@ -35,6 +35,7 @@
 	bool "KM_KIRKWOOD Board"
 	select BOARD_LATE_INIT
 	imply CMD_CRAMFS
+	imply CMD_DIAG
 	imply FS_CRAMFS
 
 config TARGET_NET2BIG_V2