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/arch/arm/mach-kirkwood/cpu.c b/arch/arm/mach-kirkwood/cpu.c
index 8f8e300..6ad2543 100644
--- a/arch/arm/mach-kirkwood/cpu.c
+++ b/arch/arm/mach-kirkwood/cpu.c
@@ -6,6 +6,7 @@
  */
 
 #include <common.h>
+#include <env.h>
 #include <netdev.h>
 #include <asm/cache.h>
 #include <asm/io.h>