Kinetis UART

Kinetis UART driver.

There are different implementations of the UART interface. The treatment of interrupts is also slightly different. The register UARTx_BDH to UARTx_C4 look almost the same. We distinguish the type of the UART using the BRFA field in the UART C4 register. Currently, only the base TX/RX functionality is available.

UART configuration example (for periph_conf.h)