zephyr: Bring in the Zephyr build
Add support for building mcuboot as a Zephyr application. This is
copied from the iotboot repo with some minor reorganization to work with
the mcuboot directory layout.
diff --git a/zephyr/prj.conf b/zephyr/prj.conf
new file mode 100644
index 0000000..5c36b1d
--- /dev/null
+++ b/zephyr/prj.conf
@@ -0,0 +1,14 @@
+CONFIG_CONSOLE_HANDLER=y
+CONFIG_PRINTK=y
+CONFIG_DEBUG=y
+
+CONFIG_MAIN_STACK_SIZE=10240
+CONFIG_MBEDTLS=y
+CONFIG_MBEDTLS_BUILTIN=y
+CONFIG_MBEDTLS_CFG_FILE="config-boot.h"
+
+### mbedTLS wants a heap
+CONFIG_HEAP_MEM_POOL_SIZE=16384
+
+CONFIG_FLASH=y
+CONFIG_SOC_FLASH_STM32F4=y