env: Drop the env_name_spec global

Add a name to the driver and use that instead of the global variable
declared by each driver.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/env/env.c b/env/env.c
index 12cd475..53a085c 100644
--- a/env/env.c
+++ b/env/env.c
@@ -54,7 +54,7 @@
 		return ENVL_UNKNOWN;
 }
 
-static struct env_driver *env_driver_lookup_default(void)
+struct env_driver *env_driver_lookup_default(void)
 {
 	enum env_location loc = env_get_default_location();
 	struct env_driver *drv;