global_data: Use less space for environment fields

Use shorter types for some of these fields to save space. Reorder to put
fields with like alignment together.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/env_internal.h

@@ -100,6 +100,7 @@ extern const char default_environment[];
 #include <env_flags.h>
 #include <search.h>
 
+/* this is stored as bits in gd->env_has_init so is limited to 16 entries */
 enum env_location {
 	ENVL_UNKNOWN,
 	ENVL_EEPROM,