[PATCH 9_9] Use "void *" not "unsigned long *" for block dev read_write buffer pointers

Block device read/write is anonymous data; there is no need to use a
typed pointer.  void * is fine.  Also add a hook for block_read functions

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

include/part.h

@@ -44,7 +44,7 @@ typedef struct block_dev_desc {
 	unsigned long	(*block_read)(int dev,
 				      unsigned long start,
 				      lbaint_t blkcnt,
-				      unsigned long *buffer);
+				      void *buffer);
 	unsigned long	(*block_write)(int dev,
 				       unsigned long start,
 				       lbaint_t blkcnt,