env: Move env_set() to env.h

Move env_set() over to the new header file.

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

board/ti/evm/evm.c

@@ -12,6 +12,7 @@
  */
 #include <common.h>
 #include <dm.h>
+#include <env.h>
 #include <ns16550.h>
 #include <netdev.h>
 #include <asm/io.h>