feat(uart): support uart module sleep retention on c6/h2/p4

components/esp_driver_uart/include/driver/uart.h

@@ -46,6 +46,13 @@ typedef struct {
         lp_uart_sclk_t lp_source_clk;       /*!< LP_UART source clock selection */
 #endif
     };
+    struct {
+#if SOC_UART_SUPPORT_SLEEP_RETENTION
+        uint32_t backup_before_sleep: 1;    /*!< If set, the driver will backup/restore the HP UART registers before entering/after exiting sleep mode.
+                                                 By this approach, the system can power off HP UART's power domain.
+                                                 This can save power, but at the expense of more RAM being consumed */
+#endif
+    } flags;                                /*!< Configuration flags */
 } uart_config_t;
 
 /**