common: Drop part.h from common header

Move this uncommon header out of the common header.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/spl/spl_ext.c b/common/spl/spl_ext.c
index 954133b..3898041 100644
--- a/common/spl/spl_ext.c
+++ b/common/spl/spl_ext.c
@@ -2,6 +2,7 @@
 
 #include <common.h>
 #include <env.h>
+#include <part.h>
 #include <spl.h>
 #include <asm/u-boot.h>
 #include <ext4fs.h>