treewide: Convert CONFIG_HOSTNAME to a string option

CONFIG_HOSTNAME is defined as a "plain" preprocessor string, but every
use is couched by __stringify(...).

Hence, convert it to a proper string option.

Signed-off-by: Mario Six <mario.six@gdsys.cc>
diff --git a/include/configs/controlcenterdc.h b/include/configs/controlcenterdc.h
index 2b7dc7c..1db18a4 100644
--- a/include/configs/controlcenterdc.h
+++ b/include/configs/controlcenterdc.h
@@ -141,7 +141,7 @@
 
 #define CONFIG_BAUDRATE 115200
 
-#define CONFIG_HOSTNAME		ccdc
+#define CONFIG_HOSTNAME		"ccdc"
 #define CONFIG_ROOTPATH		"/opt/nfsroot"
 #define CONFIG_BOOTFILE		"ccdc.img"