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/include/fb_mmc.h b/include/fb_mmc.h
index 0c58109..76ed7cd 100644
--- a/include/fb_mmc.h
+++ b/include/fb_mmc.h
@@ -6,6 +6,9 @@
 #ifndef _FB_MMC_H_
 #define _FB_MMC_H_
 
+struct blk_desc;
+struct disk_partition;
+
 /**
  * fastboot_mmc_get_part_info() - Lookup eMMC partion by name
  *