zephyr: selectable serial device for recovery

This commit adds a choice for the device to use for serial recovery.

Signed-off-by: Emanuele Di Santo <emdi@nordicsemi.no>
Signed-off-by: Andrzej Puzdrowski <andrzej.puzdrowski@nordicsemi.no>

fixup
diff --git a/boot/zephyr/Kconfig b/boot/zephyr/Kconfig
index 3502481..4b8801e 100644
--- a/boot/zephyr/Kconfig
+++ b/boot/zephyr/Kconfig
@@ -127,6 +127,23 @@
 
 if MCUBOOT_SERIAL
 
+choice
+	prompt "Serial device"
+	default BOOT_SERIAL_UART if !BOARD_NRF52840_PCA10059
+	default BOOT_SERIAL_CDC_ACM if BOARD_NRF52840_PCA10059
+
+config BOOT_SERIAL_UART
+	bool "UART"
+	# SERIAL and UART_INTERRUPT_DRIVEN already selected
+
+config BOOT_SERIAL_CDC_ACM
+	bool "CDC ACM"
+	select USB
+	select USB_DEVICE_STACK
+	select USB_CDC_ACM
+
+endchoice
+
 config BOOT_MAX_LINE_INPUT_LEN
 	int "Maximum command line length"
 	default 512