Change EFM32GG to EFM32 in README.md, images, doxygen files.
Merge branch 'efm32' of https://github.com/MarkDing/lufa-efm32 into efm32

* 'efm32' of https://github.com/MarkDing/lufa-efm32:
  Change EFM32GG to EFM32 in README.md, images, doxygen files.