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/imx27lite-common.h b/include/configs/imx27lite-common.h
index 4754614..ad9aca4 100644
--- a/include/configs/imx27lite-common.h
+++ b/include/configs/imx27lite-common.h
@@ -150,9 +150,9 @@
 		" console=ttymxc0,${baudrate}\0"			\
 	"addmtd=setenv bootargs ${bootargs} ${mtdparts}\0"		\
 	"addmisc=setenv bootargs ${bootargs}\0"				\
-	"u-boot=" __stringify(CONFIG_HOSTNAME) "/u-boot.bin\0"		\
+	"u-boot=" CONFIG_HOSTNAME "/u-boot.bin\0"		\
 	"kernel_addr_r=a0800000\0"					\
-	"bootfile=" __stringify(CONFIG_HOSTNAME) "/uImage\0"		\
+	"bootfile=" CONFIG_HOSTNAME "/uImage\0"		\
 	"rootpath=/opt/eldk-4.2-arm/arm\0"				\
 	"net_nfs=tftp ${kernel_addr_r} ${bootfile};"			\
 		"run nfsargs addip addtty addmtd addmisc;"		\