env: move extern environment[] to environment.h

Extract all extern declarations for environment out of c files
into the environment.h header.

Signed-off-by: Igor Grinberg <grinberg@compulab.co.il>
diff --git a/include/environment.h b/include/environment.h
index 20775da..951803f 100644
--- a/include/environment.h
+++ b/include/environment.h
@@ -154,6 +154,10 @@
 	unsigned char	data[ENV_SIZE]; /* Environment data		*/
 } env_t;
 
+#ifdef ENV_IS_EMBEDDED
+extern env_t environment;
+#endif /* ENV_IS_EMBEDDED */
+
 extern const unsigned char default_environment[];
 
 #ifndef DO_DEPS_ONLY