zephyr: add zephyr's sanitycheck description

Added sample.yaml which is required for automatic building
mcuboot using zephyr sanitycheck.

Can be run by zephyr sanitycheck locally using
--testcase-root=/path/to/mcuboot/boot/zephyr
to make it detect the sample.yaml added.

Signed-off-by: Andrzej Puzdrowski <andrzej.puzdrowski@nordicsemi.no>
Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>
diff --git a/boot/zephyr/serial_recovery.conf b/boot/zephyr/serial_recovery.conf
new file mode 100644
index 0000000..ddd08fc
--- /dev/null
+++ b/boot/zephyr/serial_recovery.conf
@@ -0,0 +1,3 @@
+CONFIG_MCUBOOT_SERIAL=y
+CONFIG_BOOT_SERIAL_UART=y
+CONFIG_UART_CONSOLE=n