Gecko SDK fork

This is a fork of some of the Gecko SDK components from Silicon Laboratories. It includes fixes and new features that can be useful for everyone in the community.

Silicon Laboratories and its employees are encouraged to use these patches and include them in their own releases.

Change log

UARTDRV

• Fix various issues regarding building with C++ compilers
• Fix UARTDRV_Abort, previously UARTDRV was unable to perform any more transmit or receive operations because UARTDRV_Abort did not clean up after itself.
• Add ability to work with half-duplex mode, when the trasmitter and receiver are on a single pin.
• Fix LEUART clock source selection issue
• Various minor improvements