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/common/splash_source.c b/common/splash_source.c
index 8f276a3..d37b4b3 100644
--- a/common/splash_source.c
+++ b/common/splash_source.c
@@ -7,6 +7,7 @@
 
 #include <common.h>
 #include <bmp_layout.h>
+#include <env.h>
 #include <errno.h>
 #include <fs.h>
 #include <fdt_support.h>