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/bcm_northstar2.h b/include/configs/bcm_northstar2.h
index 9c66643..f0eba6b 100644
--- a/include/configs/bcm_northstar2.h
+++ b/include/configs/bcm_northstar2.h
@@ -9,7 +9,7 @@
 
 #include <linux/sizes.h>
 
-#define CONFIG_HOSTNAME				northstar2
+#define CONFIG_HOSTNAME				"northstar2"
 
 /* Physical Memory Map */
 #define V2M_BASE				0x80000000