sdcard: handle CMD54 (SDIO)

Linux uses it to poll the bus before polling for a card.
Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: NAlistair Francis <alistair.francis@xilinx.com>
Message-id: 20180215221325.7611-10-f4bug@amsat.org
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

hw/sd/sd.c

@@ -1371,9 +1371,8 @@ static sd_rsp_type_t sd_normal_command(SDState *sd,
         }
         break;
 
-    case 52:
-    case 53:
-        /* CMD52, CMD53: reserved for SDIO cards
+    case 52 ... 54:
+        /* CMD52, CMD53, CMD54: reserved for SDIO cards
          * (see the SDIO Simplified Specification V2.0)
          * Handle as illegal command but do not complain
          * on stderr, as some OSes may use these in their