F1 pinmap: input mode may be associated with an alternate function

On F1 specifically, input alternate functions must configure GPIO
in input mode.
Example: on F103 PinMap_UART_RX
{PB_7, USART1, STM_PIN_DATA(STM_MODE_INPUT, GPIO_PULLUP, AFIO_USART1_ENABLE)},

Author: ABOSTM

Diff for: libraries/SrcWrapper/src/stm32/pinmap.c

@@ -121,6 +121,10 @@ void pin_function(PinName pin, int function)
   switch (mode) {
     case STM_PIN_INPUT:
       ll_mode = LL_GPIO_MODE_INPUT;
+#if defined(STM32F1xx)
+      // on F1 family, input mode may be associated with an alternate function
+      pin_SetAFPin(gpio, pin, afnum);
+#endif
       break;
     case STM_PIN_OUTPUT:
       ll_mode = LL_GPIO_MODE_OUTPUT;