hw/sd: sd: Remove duplicated codes in single/multiple block read/write

hw/sd: sd: Remove duplicated codes in single/multiple block read/write

The single block read (CMD17) codes are the same as the multiple
block read (CMD18). Merge them into one. The same applies to single
block write (CMD24) and multiple block write (CMD25).

Signed-off-by: Bin Meng <[email protected]>
Tested-by: Philippe Mathieu-Daudé <[email protected]>
Acked-by: Alistair Francis <[email protected]>
Message-Id: <20210128063035[email protected]>
Signed-off-by: Philippe Mathieu-Daudé <[email protected]>