Moved simultaneous reading and writing into SPI; removed it from I2C and UART

include/sta/bus/spi/spi.hpp

@@ -31,6 +31,15 @@ namespace sta
          */
         SPI(const SPISettings & settings, Mutex * mutex = nullptr);
 
+        /**
+		 * @brief Send and receive data simultaneously.
+		 *
+		 * @param txBuffer  Send buffer
+		 * @param rxBuffer  Receive buffer
+		 * @param size      Number of bytes to transfer
+		 */
+		virtual void transfer(const uint8_t * txBuffer, uint8_t * rxBuffer, size_t size) = 0;
+
         /**
          * @brief Get %SPI interface settings.
          *