driver: serial: stm32u5: DMAT Errata behavior valid only on some SoCs

Workaround for DMAT errata was applied on all SoCs declaring STM32U5
DMA compatible.
This errata has been fixed in later SoCs revisions and should not be
applied anymore as this can cause compatibility issues with power mgmt
(can not enter STOP1 in some cases).

Declare a specific Kconfig symbol to restrict the workaround only to the
set of SoCs impacted by the issue and requiring workaround.

Note that I preferred using Kconfig over device tree since it doesn't feel
right to declare a compatible on a silicon bug base.

Signed-off-by: Erwan Gouriou <erwan.gouriou@st.com>
diff --git a/drivers/serial/uart_stm32.c b/drivers/serial/uart_stm32.c
index 5c1ff75..dd79612 100644
--- a/drivers/serial/uart_stm32.c
+++ b/drivers/serial/uart_stm32.c
@@ -1321,7 +1321,7 @@
 
 static inline void uart_stm32_dma_tx_disable(const struct device *dev)
 {
-#if DT_HAS_COMPAT_STATUS_OKAY(st_stm32u5_dma)
+#ifdef CONFIG_UART_STM32U5_ERRATA_DMAT
 	ARG_UNUSED(dev);
 
 	/*
@@ -1333,7 +1333,7 @@
 	const struct uart_stm32_config *config = dev->config;
 
 	LL_USART_DisableDMAReq_TX(config->usart);
-#endif /* ! st_stm32u5_dma */
+#endif
 }
 
 static inline void uart_stm32_dma_rx_enable(const struct device *dev)
@@ -1633,9 +1633,9 @@
 		data->dma_tx.counter = tx_buffer_length - stat.pending_length;
 	}
 
-#if DT_HAS_COMPAT_STATUS_OKAY(st_stm32u5_dma)
+#ifdef CONFIG_UART_STM32U5_ERRATA_DMAT
 	dma_suspend(data->dma_tx.dma_dev, data->dma_tx.dma_channel);
-#endif /* st_stm32u5_dma */
+#endif
 	dma_stop(data->dma_tx.dma_dev, data->dma_tx.dma_channel);
 	async_evt_tx_abort(data);