drivers: i2s: Add DMA busy function

Add the function ll_func_i2s_dma_busy to be able to check the
transmission of all the DMA TX packet.

Signed-off-by: IBEN EL HADJ MESSAOUD Marwa <marwa.ibenelhadjmessaoud-ext@st.com>

drivers/i2s/i2s_ll_stm32.h

@@ -61,4 +61,16 @@ struct i2s_stm32_data {
 	struct stream tx;
 };
 
+/* checks that DMA Tx packet is fully transmitted over the I2S */
+static inline uint32_t ll_func_i2s_dma_busy(SPI_TypeDef *i2s)
+{
+#if DT_HAS_COMPAT_STATUS_OKAY(st_stm32h7_i2s)
+	return LL_SPI_IsActiveFlag_TXC(i2s);
+#else
+	/* the I2S Tx empty and busy flags are needed */
+	return (LL_SPI_IsActiveFlag_TXE(i2s) &&
+		!LL_SPI_IsActiveFlag_BSY(i2s));
+#endif
+}
+
 #endif	/* _STM32_I2S_H_ */