STM32: F1 GPIO: Enable AFIO clock

It is required to enable AFIO clock before using __HAL_AFIO_REMAP_xy
macros, which was missing here. Without clocks enable, the remap
actually doesn't occur. This would possibly cause some PIOs (part of
PB_3, PB_4, PA_13, PA_14, PA_15) to not behave as expected.

In most cases AFIO clock was enabled in stm_pin_SetAFPin function, so
that this bug was not visible. But there were few cases left were
stm_pin_DisconnectDebug would be called first. A typical case was
with GCC_ARM in case a DigitalInOut variable is declared as global.

targets/TARGET_STM/TARGET_STM32F1/pin_device.h

@@ -37,6 +37,9 @@ extern const uint32_t ll_pin_defines[16];
 
 static inline void stm_pin_DisconnectDebug(PinName pin)
 {
+    // Enable AFIO clock
+    __HAL_RCC_AFIO_CLK_ENABLE();
+
     // Disconnect JTAG-DP + SW-DP signals.
     // Warning: Need to reconnect under reset
     if ((pin == PA_13) || (pin == PA_14)) {