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/M52277EVB.h b/include/configs/M52277EVB.h
index 7798b06..2e2e512 100644
--- a/include/configs/M52277EVB.h
+++ b/include/configs/M52277EVB.h
@@ -31,7 +31,7 @@
  */
 #define CONFIG_BOOTP_BOOTFILESIZE
 
-#define CONFIG_HOSTNAME			M52277EVB
+#define CONFIG_HOSTNAME			"M52277EVB"
 #define CONFIG_SYS_UBOOT_END		0x3FFFF
 #define	CONFIG_SYS_LOAD_ADDR2		0x40010007
 #ifdef CONFIG_SYS_STMICRO_BOOT