soc: esp32s2: add initial soc support files for esp32s2

by adding specific soc files for esp32s2 bring-up, such as:
- linker script
- soc initialization code
- initial device tree source files
- esp32s2 saola board support.

Signed-off-by: Glauber Maroto Ferreira <glauber.ferreira@espressif.com>