add: FPC connector skeleton usart. Not working but if will be a starting point for those who might want to help out with it.

common/usart.h

@@ -0,0 +1,21 @@
+#ifndef __USART_H
+#define __USART_H
+
+#include <stddef.h>
+#include "proxmark3.h"
+
+//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~//
+extern void Dbprintf(const char *fmt, ...);
+
+void usart_init(void);
+void usart_close(void);
+
+uint32_t usart_rx_ready();
+uint32_t usart_tx_ready();
+
+uint8_t usart_read(uint32_t timeout);
+uint8_t usart_readbuffer(uint8_t *data, size_t len);
+
+void usart_write( uint8_t data, uint32_t timeout);
+uint8_t usart_writebuffer(uint8_t *data, size_t len, uint32_t timeout);
+#endif