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>

cmd/bootefi.c

@@ -11,6 +11,7 @@
 #include <dm.h>
 #include <efi_loader.h>
 #include <efi_selftest.h>
+#include <env.h>
 #include <errno.h>
 #include <linux/libfdt.h>
 #include <linux/libfdt_env.h>