/dev/sdio/slot0

This allows access to the front SD slot.

SD_GetDeviceStatus
ios_ioctl( sd_fd, 0x0B, 0, 0, buffer, 4);

SD_ResetDevice
ios_ioctl( sd_fd, 4, 0, 0, buffer, 4);

SD_GetOCRegister
ios_ioctl( sd_fd, 0xC, 0, 0, buffer, 4);

SD_GetHCRegister (untested iirc)
((u32*)inbuf)[0] = 0x28;
((u32*)inbuf)[3] = 1;
((u32*)inbuf)[4] = 0;

ios_ioctl( sd_fd, 2, inbuf, 0x18, outbuf, 4);

SD_SendCMD
I couldn't get this function working maybe someone else has more luck

((u32*)inbuf)[0]=0;	//SD CMD
((u32*)inbuf)[1]=0;
((u32*)inbuf)[2]=0;
((u32*)inbuf)[3]=0;	//offset
((u32*)inbuf)[4]=0;	//buffer
((u32*)inbuf)[5]=0;	//blocks to write
((u32*)inbuf)[6]=0;	//sector size
((u32*)inbuf)[7]=0;

ios_ioctl( sd_fd, 7, inbuf, 0x24, outbuf, 0x10);