Toupstream

Alan

This branch tidies up the IDE driver a little and splits out the MBR partition parser. It adds a (hopefully!) reasonably generic SD card driver, where the platform just needs to provide a few simple SPI functions (which could use either dedicated SPI hardware or just simple GPIO). Finally it adds a SPI driver for n8vem-mark4 using the CSIO device in the Z180, giving that platform SD card support.