Driver implementation callbacks.
| UART_dmaOpenFxn UART_DmaFxns::dmaOpenFxn |
| UART_dmaTransferWriteFxn UART_DmaFxns::dmaTransferWriteFxn |
| UART_dmaTransferReadFxn UART_DmaFxns::dmaTransferReadFxn |
| UART_dmaCloseFxn UART_DmaFxns::dmaCloseFxn |
| UART_dmaDisableChannelFxn UART_DmaFxns::dmaDisableChannelFxn |