teensy: Add own uart.h to not rely on stm32's version of the file.

ports/teensy/uart.h

+#ifndef MICROPY_INCLUDED_TEENSY_UART_H
+#define MICROPY_INCLUDED_TEENSY_UART_H
+
+typedef enum {
+    PYB_UART_NONE = 0,
+} pyb_uart_t;
+
+typedef struct _pyb_uart_obj_t pyb_uart_obj_t;
+
+extern const mp_obj_type_t pyb_uart_type;
+
+mp_uint_t uart_rx_any(pyb_uart_obj_t *uart_obj);
+int uart_rx_char(pyb_uart_obj_t *uart_obj);
+void uart_tx_strn(pyb_uart_obj_t *uart_obj, const char *str, uint len);
+
+#endif // MICROPY_INCLUDED_TEENSY_UART_H