Import YEEP-144 library 1.2 sources

Source-only snapshot of the 1.2 release. Drivers/ (the vendored ST HAL and
CMSIS) is excluded at 173 MB; fetch it from STMicroelectronics/STM32CubeH5 to
build.

YEEP144lib/include/YEEP144_PiSPI.h

@@ -0,0 +1,18 @@
+#ifndef __YEEP144_PISPI_H
+#define __YEEP144_PISPI_H
+
+// This value define the size of the transfer buffers. 
+// It needs to match what is set on the Pi side so the correct amount of data is transferred each time
+#define PISPI_BUFFER_SIZE 256
+
+// Extern the buffer arrays so they are accessible from other files
+extern uint8_t PiSPIRxBuf[PISPI_BUFFER_SIZE];
+extern uint8_t PiSPITxBuf[PISPI_BUFFER_SIZE];
+
+void YEEP144_PiSPI_Init(void);
+void YEEP144_PiSPI_SetReady(void);
+void YEEP144_PiSPI_ResetReady(void);
+void YEEP144_PiSPI_LoadTx(void);
+void YEEP144_PiSPI_TxRxHandler(void);
+
+#endif