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

src/bus/spi/device.cpp

@@ -12,6 +12,15 @@ namespace sta
         STA_ASSERT(csPin != nullptr);
     }
 
+    void SPIDevice::transfer(const uint8_t * txBuffer, uint8_t * rxBuffer, size_t size)
+	{
+		STA_ASSERT(intf_->isAcquired());
+		STA_ASSERT(txBuffer != nullptr);
+		STA_ASSERT(rxBuffer != nullptr);
+
+		intf_->transfer(txBuffer, rxBuffer, size);
+	}
+
     const SPISettings & SPIDevice::settings() const
     {
         return intf_->settings();