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/UCP1020.h b/include/configs/UCP1020.h
index 0cc3af7..489e4e3 100644
--- a/include/configs/UCP1020.h
+++ b/include/configs/UCP1020.h
@@ -469,7 +469,7 @@
 
 #endif
 
-#define CONFIG_HOSTNAME		UCP1020
+#define CONFIG_HOSTNAME		"UCP1020"
 #define CONFIG_ROOTPATH		"/opt/nfsroot"
 #define CONFIG_BOOTFILE		"uImage"
 #define CONFIG_UBOOTPATH	u-boot.bin /* U-Boot image on TFTP server */