blk: Remove various places that do flush cache after read

All these places seem to inherit the codes from the MMC driver where
a FIXME was put in the comment. However the correct operation after
read should be cache invalidate, not flush.

The underlying drivers should be responsible for the cache operation.
Remove these codes completely.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Reviewed-by: York Sun <york.sun@nxp.com>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: York Sun <york.sun@nxp.com>

cmd/mmc.c

@@ -293,8 +293,6 @@ static int do_mmc_read(cmd_tbl_t *cmdtp, int flag,
 	       curr_device, blk, cnt);
 
 	n = blk_dread(mmc_get_blk_desc(mmc), blk, cnt, addr);
-	/* flush cache after read */
-	flush_cache((ulong)addr, cnt * 512); /* FIXME */
 	printf("%d blocks read: %s\n", n, (n == cnt) ? "OK" : "ERROR");
 
 	return (n == cnt) ? CMD_RET_SUCCESS : CMD_RET_FAILURE;