Linux HAL updates

1. The type correction was merged as part of
   eive/fsfw#7 in the
   EIVE project. Quotation of PR

definition of getSpiParameters is `void getSpiParameters(spi::SpiModes& spiMode, uint32_t& spiSpeed, UncommonParameters* parameters = nullptr) const;`.

Here, size_t spiSpeed is passed, which implicitely gets converted to a temporary, which can not be bound to uint32_t& and, at least in gcc 9.3.0, leads to a compiler error.

2. Allow flushing the UART buffers

@@ -446,0 +452,4 @@
+        return NULLPOINTER;
+    }
+    deviceFile = uartCookie->getDeviceFile();
+    uartDeviceMapIter = uartDeviceMap.find(deviceFile);