Features
   * The device for reading entropy on platforms without a dedicated system
     call can now be configured with MBEDTLS_PLATFORM_DEV_RANDOM or
     mbedtls_platform_dev_random.

Security
   * The default device for reading entropy on platforms without a dedicated
     system call is now /dev/random instead of /dev/urandom. This is safer
     on Linux in case the application runs early after the kernel boots,
     but may block needlessly on Linux <= 5.6. Reported by supers1ngular
     (BayLibre).