PSoC4 SCB UART with interrupts

The SCB UART is configured to generate an internal interrupt on Rx FIFO not empty. A custom interrupt handler is already registered and will be called when the interrupt happens.

Characters received over UART will be pushed into a circular buffer in the custom interrupt handler.

Testing:

Enter a text in the UART terminal and end it with '.'. The whole text will be immediately printed back on the terminal.