* SiM3 SDK 
* USB stack base on LUFA
* FAT 12/16/32 support base on Fatfs
* SD card driver support.
* MCU platform is SiM3U167 Arm Cortex M3 core.

Status
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* USB CDC class has been tested and works well.
* Three VCP support added
* Other classes need to be tested in future.

* SD card SPI driver was done, not implement DMA support yet.
* FATFS read/write file and directory list work OK.