samples: stm32: move board-specific STM32 UART sample

The STM32 single-wire UART sample should live with board-specific
samples.

Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>

samples/boards/stm32/uart/single_wire/README.rst

@@ -20,7 +20,7 @@ Building and Running
 Build and flash as follows, replacing ``stm32f3_disco`` with your board:
 
  .. zephyr-app-commands::
-    :zephyr-app: samples/drivers/uart/stm32/single_wire
+    :zephyr-app: samples/boards/stm32/uart/single_wire
     :board: stm32f3_disco
     :goals: build flash
     :compact:

samples/boards/stm32/uart/single_wire/sample.yaml

@@ -1,7 +1,7 @@
 sample:
   name: STM32 Single Wire UART sample
 tests:
-  sample.drivers.uart.stm32.single_wire:
+  sample.boards.stm32.uart.single_wire:
     platform_allow: stm32f3_disco
     tags:
       - drivers