add esp32s2 saola bsp

update cdc_msc_freertos main.c to work with esp32s2
add CMake file

examples/device/cdc_msc_freertos/CMakeLists.txt

@@ -0,0 +1,10 @@
+# The following five lines of boilerplate have to be in your project's
+# CMakeLists in this exact order for cmake to work correctly
+cmake_minimum_required(VERSION 3.5)
+
+# example src directory
+set(EXTRA_COMPONENT_DIRS "src")
+
+include($ENV{IDF_PATH}/tools/cmake/project.cmake)
+
+project(blink)