FPC: got RX working, got client over usart somehow working..., see detailed commit msg

* using WITH_FPC:
  * activate basic usart
  * no double buffer for now, no interrupt
  * usart_dataavailable/usart_readbuffer/usart_writebuffer, to demo it:
    * pm3 client over USB, minicom over usart
    * analyse a d 414243
* using WITH_FPC_HOST:
  * it implies WITH_FPC as it's based on it
  * control pm3 with client over usart
  * EXPERIMENTAL! still some frame desync issues
  * you can connect both from usart & USB with two pm3 clients
    * actually you *have* to connect USB for the moment because
      it's used to send debug messages about buggy usart... See Dbprintf_usb below
  * "sessions": msgs are directed to the latest client to have sent a cmd
  * Dbprintf_usb macro to send msgs to USB client to help debugging usart...
  * We now have an option to run client at different speed as usart is 115200:
    client/proxmark3 /dev/ttyUSB0 -b 115200
  * Consequently, argc,argv handling is a bit revamped, it was so messy...
  * USB and flashing are still at 460800, don't try flashing over usart yet ^^

client/flash.c

@@ -321,7 +321,7 @@ static int enter_bootloader(char *serial_port_name) {
         // Let time to OS to make the port disappear
         msleep(1000);
 
-        bool opened = OpenProxmark(serial_port_name, true, 60, true);
+        bool opened = OpenProxmark(serial_port_name, true, 60, true, FLASHMODE_SPEED);
         if (opened) {
             fprintf(stdout, " " _GREEN_("Found") "\n");
             return 0;