hw/sd/sdcard: Remove SEND_DSR dead case (CMD4)

hw/sd/sdcard: Remove SEND_DSR dead case (CMD4)

The CSD::CSR_IMP bit defines whether the Driver Stage
Register (DSR) is implemented or not. We do not set
this bit in CSD:

    static void sd_set_csd(SDState *sd, uint64_t size)
    {
        ...
        if (size <= SDSC_MAX_CAPACITY) { /* Standard Capacity SD */
            ...
            sd->csd[6] = 0xe0 |     /* Partial block for read allowed */
                ((csize >> 10) & 0x03);
            ...
        } else {                    /* SDHC */
            ...
            sd->csd[6] = 0x00;
            ...
        }
        ...
    }

The sd_normal_command() switch case for the SEND_DSR
command do nothing and fallback to "illegal command".
Since the command is mandatory (although the register
isn't...) call the sd_cmd_unimplemented() handler.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Message-Id: <20240628070216.92609-43-philmd@linaro.org>