[stm32] Fix initialization of FDCAN message RAM

After power-on the FDCAN message RAM is filled with non-zero invalid
data. In some cases the CAN filter region contains well-formed entries
which cause inadvertent reception or rejection of messages.

To prevent this message RAM sections are now zeroed out on the first
initialization of the respective FDCAN instance.

src/modm/platform/can/common/fdcan/message_ram.hpp

@@ -270,7 +270,15 @@ class MessageRam
 	{
 		return messageRamWord(FilterListExtended(), index * ExtendedFilterSize);
 	}
+
 public:
+	static void
+	zeroAllData()
+	{
+		for (uint32_t word = 0; word < Config.totalSectionWords(); ++word)
+			*messageRamWord(RamBase, word) = 0;
+	}
+
 	/// Write TX element headers to TX queue
 	static void
 	writeTxHeaders(uint8_t putIndex, CommonFifoHeader_t common, TxFifoHeader_t tx)

src/modm/platform/can/stm32-fdcan/can.cpp.in

@@ -216,6 +216,10 @@ modm::platform::Fdcan{{ id }}::initializeWithPrescaler(
 	static_assert(MessageRam::Config.txFifoSectionOffset() + MessageRam::Config.txFifoSectionWords() == MessageRam::Config.totalSectionWords());
 
 	MessageRam::setRamBase(SRAMCAN_BASE + (messageRamBaseWords * MessageRam::RamWordSize));
+	if (!messageRamInitialized_) {
+		MessageRam::zeroAllData();
+		messageRamInitialized_ = true;
+	}
 
 %% if target["family"] == "h7"
 	// Configure number of elements in each RAM section

src/modm/platform/can/stm32-fdcan/can.hpp.in

@@ -111,6 +111,7 @@ private:
 	using MessageRam = fdcan::MessageRam<{{ id - 1 }}, fdcan::Fdcan{{id}}MessageRamConfig>;
 
 	static inline volatile ErrorCallback errorCallback_ = nullptr;
+	static inline bool messageRamInitialized_{false};
 
 	static void
 	initializeWithPrescaler(