Request to add scimmc driver to dreamshell

[SWAT]

It has long been thought to add SPI driver on internal SCI (looks like it's can be drive native SPI protocol without bit-bang), but the feasibility of this is questionable, since there is much more productive mod - G1-ATA.
For your mod need open console box and solder wires, so maybe best way do G1-ATA instead? Current SPI mod is good because it can be used without modification of the console, so I'll keep it forever.
If you can solder wires - why not do G1-ATA, it's best choice. But just for fun I can do SPI for SCI, why not
Low speed (~500kHz) need only for initialization of SD, after init, it's may increased to max speed. But I'm not sure what is the max speed, need test.