1. Add SD card driver (SPI mode)
2. Add ELM ChaN FatFs support (Please read "Readme.txt")
   - Warning: FatFs is really FAT! (35KB)
3. Upgrade EFM32 libraries (CMSIS and efm32lib) to version 2.0.0
4. Merge all of the C source code in "libcpu\arm\cortex-m3\" into "cpuport.c"
5. Merge all of the assembly source code in "libcpu\arm\cortex-m3\" into "context_gcc.S" (except "start_gcc.S")

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@1525 bbd45198-f89e-11dd-88c7-29a3b14d5316