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/kmp204x.h b/include/configs/kmp204x.h
index 8bb3571..37a33e5 100644
--- a/include/configs/kmp204x.h
+++ b/include/configs/kmp204x.h
@@ -10,12 +10,12 @@
 
 /* KMLION1 */
 #if defined(CONFIG_KMLION1)
-#define CONFIG_HOSTNAME		kmlion1
+#define CONFIG_HOSTNAME		"kmlion1"
 #define CONFIG_KM_BOARD_NAME	"kmlion1"
 
 /* KMCOGE4 */
 #elif defined(CONFIG_KMCOGE4)
-#define CONFIG_HOSTNAME		kmcoge4
+#define CONFIG_HOSTNAME		"kmcoge4"
 #define CONFIG_KM_BOARD_NAME	"kmcoge4"
 
 #else