env_nowhere: Move conditional compilation to Makefile

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
diff --git a/common/Makefile b/common/Makefile
index e171ae0..cf861c5 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -57,7 +57,7 @@
 COBJS-$(CONFIG_ENV_IS_IN_NVRAM) += env_nvram.o
 COBJS-$(CONFIG_ENV_IS_IN_ONENAND) += env_onenand.o
 COBJS-$(CONFIG_ENV_IS_IN_SPI_FLASH) += env_sf.o
-COBJS-y += env_nowhere.o
+COBJS-$(CONFIG_ENV_IS_NOWHERE) += env_nowhere.o
 
 # command
 COBJS-$(CONFIG_CMD_AMBAPP) += cmd_ambapp.o