env: Move env_set_hex() to env.h

Move env_set_hex() over to the new header file along with env_set_addr()
which uses it.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/cmd/tpm-v1.c b/cmd/tpm-v1.c
index b75e093..2807331 100644
--- a/cmd/tpm-v1.c
+++ b/cmd/tpm-v1.c
@@ -4,6 +4,7 @@
  */
 
 #include <common.h>
+#include <env.h>
 #include <malloc.h>
 #include <asm/unaligned.h>
 #include <tpm-common.h>