common: Drop part.h from common header

Move this uncommon header out of the common header.

Signed-off-by: Simon Glass <sjg@chromium.org>

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>

common/spl/spl_mmc.c

@@ -7,6 +7,7 @@
  */
 #include <common.h>
 #include <dm.h>
+#include <part.h>
 #include <spl.h>
 #include <linux/compiler.h>
 #include <errno.h>