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/compulab/cl-som-imx7/cl-som-imx7.c

@@ -8,6 +8,7 @@
  */
 
 #include <common.h>
+#include <env.h>
 #include <environment.h>
 #include <mmc.h>
 #include <phy.h>

board/compulab/cm_fx6/cm_fx6.c

@@ -11,6 +11,7 @@
 #include <ahci.h>
 #include <dm.h>
 #include <dwc_ahsata.h>
+#include <env.h>
 #include <environment.h>
 #include <fsl_esdhc_imx.h>
 #include <miiphy.h>

board/compulab/cm_t335/cm_t335.c

@@ -8,6 +8,7 @@
  */
 
 #include <common.h>
+#include <env.h>
 #include <environment.h>
 #include <errno.h>
 #include <miiphy.h>

board/compulab/cm_t35/cm_t35.c

@@ -12,6 +12,7 @@
  */
 
 #include <common.h>
+#include <env.h>
 #include <environment.h>
 #include <status_led.h>
 #include <netdev.h>

board/compulab/cm_t54/cm_t54.c

@@ -8,6 +8,7 @@
  */
 
 #include <common.h>
+#include <env.h>
 #include <environment.h>
 #include <fdt_support.h>
 #include <usb.h>