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/fastboot/fb_common.c

@@ -11,6 +11,7 @@
  */
 
 #include <common.h>
+#include <env.h>
 #include <fastboot.h>
 #include <net/fastboot.h>
 

drivers/fastboot/fb_getvar.c

@@ -4,6 +4,7 @@
  */
 
 #include <common.h>
+#include <env.h>
 #include <fastboot.h>
 #include <fastboot-internal.h>
 #include <fb_mmc.h>

drivers/fastboot/fb_mmc.c

@@ -6,6 +6,7 @@
 #include <config.h>
 #include <common.h>
 #include <blk.h>
+#include <env.h>
 #include <fastboot.h>
 #include <fastboot-internal.h>
 #include <fb_mmc.h>