Clean up various C source and headers to appease -Wstrict-prototypes

In C, func() is a function taking an unspecified number of arguments,
vs func(void) a function taking no arguments. In C++ both forms indicate
"no arguments."

Update these headers to use the (void) form, which is correct in both
languages and avoids complaints when -Wstrict-prototypes is specified.

src/rp2_common/hardware_uart/include/hardware/uart.h

@@ -413,7 +413,7 @@ void uart_set_translate_crlf(uart_inst_t *uart, bool translate);
 /*! \brief Wait for the default UART'S TX fifo to be drained
  *  \ingroup hardware_uart
  */
-static inline void uart_default_tx_wait_blocking() {
+static inline void uart_default_tx_wait_blocking(void) {
     uart_tx_wait_blocking(uart_default);
 }