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/input/input.c

@@ -9,6 +9,7 @@
 #include <common.h>
 #include <console.h>
 #include <dm.h>
+#include <env.h>
 #include <errno.h>
 #include <stdio_dev.h>
 #include <input.h>