tests: drivers: uart: async_dual: Extend testing

Extend test with a mode where HWFC is off and receiver is providing
buffers on time. In that case receiver should be able to continuously
receive data without losing any byte (even without HWFC). Additionally,
TX data is chopped to verify that receiver does not loose bytes when
new TX data collides with detected RX timeout.

Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>

Author: nordic-krch

tests/drivers/uart/uart_async_dual/Kconfig

@@ -16,5 +16,13 @@ config PM_RUNTIME_IN_TEST
 	select PM_DEVICE
 	select PM_DEVICE_RUNTIME
 
+config TEST_CHOPPED_TX
+	bool "Test chopped TX data"
+	default y
+	help
+	  When enabled then test cases that transmits TX packets in random chunks are
+	  performed. Some driver implementation do not support case when new TX data
+	  collides with handling of the RX timeout.
+
 # Include Zephyr's Kconfig
 source "Kconfig"