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/drivers/mmc/mmc.c b/drivers/mmc/mmc.c
index 523c055..ca62bb9 100644
--- a/drivers/mmc/mmc.c
+++ b/drivers/mmc/mmc.c
@@ -8,6 +8,7 @@
 
 #include <config.h>
 #include <common.h>
+#include <blk.h>
 #include <command.h>
 #include <dm.h>
 #include <dm/device-internal.h>