env: Move env_get() to env.h

Move env_get() over to the new header file.

Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Signed-off-by: Simon Glass <sjg@chromium.org>

drivers/reset/reset-socfpga.c

@@ -16,6 +16,7 @@
 #include <dm.h>
 #include <dm/lists.h>
 #include <dm/of_access.h>
+#include <env.h>
 #include <reset-uclass.h>
 #include <linux/bitops.h>
 #include <linux/io.h>