boards: mps2_an385: Enable SLIP networking

mps2_an385 is enabled for networking -> default networking is SLIP ->
SLIP selects UART_PIPE -> UART_PIPE requires UART_PIPE_ON_DEV defined
-> undefined leads to error on building some samples.

Fix all of these issues.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>

Author: pfalcon

boards/arm/mps2_an385/mps2_an385.dts

@@ -11,6 +11,7 @@
 	chosen {
 		zephyr,console = &uart0;
 		zephyr,shell-uart = &uart0;
+		zephyr,uart-pipe = &uart1;
 		zephyr,sram = &sram0;
 		zephyr,flash = &flash0;
 	};

boards/arm/mps2_an385/mps2_an385.yaml

@@ -7,5 +7,7 @@ toolchain:
   - zephyr
   - gnuarmemb
   - xtools
+supported:
+  - netif:slip
 testing:
   default: true