soc: silabs: siwx91x: add missing kconfig for ns16550 driver variant

The ns16550 UART driver has multiple variant Kconfig options. To
successfully run the uart_basic_api test, the correct variant must be
selected. This commit adds the missing Kconfig option.

Signed-off-by: Martin Hoff <[email protected]>

Author: Martinhoff-maker

soc/silabs/silabs_siwx91x/Kconfig.defconfig

@@ -13,6 +13,9 @@ configdefault SYS_CLOCK_TICKS_PER_SEC
 	default 128 if !TICKLESS_KERNEL && SILABS_SLEEPTIMER_TIMER
 	default 1024 if SILABS_SLEEPTIMER_TIMER
 
+configdefault UART_NS16550_DW8250_DW_APB
+	default y
+
 config WISECONNECT_NETWORK_STACK
 	bool
 	select CMSIS_RTOS_V2