Add output of build version in ssl_server2
Add output of build version in ssl_server2

Usage:
- By default, build version is printed out in the beginning of
ssl_server2 application.
- ./ssl_server2 build_version=1 only prints build verison and stop

Signed-off-by: Yanray Wang <dc5ade0068f3380c5c6e9f819921d28cea5625cd@arm.com>

ARMmbed/mbedtls,Mbed-TLS/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,ARMmbed/mbedtls