mbedtls: update to 2.16.11
Switched to AUTORELEASE to avoid manual increments.
Release notes:
https://github.com/ARMmbed/mbedtls/releases/tag/v2.16.11
Signed-off-by: Rosen Penev <rosenp@gmail.com>
(cherry picked from commit fcfd741eb83520e496eb09de5f8b2f2b62792a80)