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>
diff --git a/arch/arm/mach-imx/mx7/soc.c b/arch/arm/mach-imx/mx7/soc.c
index 1b4bbc5..3b8e1ba 100644
--- a/arch/arm/mach-imx/mx7/soc.c
+++ b/arch/arm/mach-imx/mx7/soc.c
@@ -14,6 +14,7 @@
 #include <asm/arch/imx-rdc.h>
 #include <asm/arch/crm_regs.h>
 #include <dm.h>
+#include <env.h>
 #include <imx_thermal.h>
 #include <fsl_sec.h>
 #include <asm/setup.h>