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>
diff --git a/board/broadcom/bcm28155_ap/bcm28155_ap.c b/board/broadcom/bcm28155_ap/bcm28155_ap.c
index 6faeb6a..8761638 100644
--- a/board/broadcom/bcm28155_ap/bcm28155_ap.c
+++ b/board/broadcom/bcm28155_ap/bcm28155_ap.c
@@ -6,6 +6,7 @@
 #include <common.h>
 #include <asm/io.h>
 #include <asm/mach-types.h>
+#include <env.h>
 #include <mmc.h>
 #include <asm/kona-common/kona_sdhci.h>
 #include <asm/kona-common/clk.h>