fix(lib/mbedtls): cmake rules and mbedtls targets

- Include targets from mbedtls/library instead of including top level
  CMakeLists.txt
- Move mbedtls configs to mbedtls_config.h
- Remove stale build option MbedTLS_BUILD_TYPE from documentation

Signed-off-by: Arunachalam Ganapathy <arunachalam.ganapathy@arm.com>
Change-Id: I7096ef6df9339c2c490450f72ec91b681b32543e
4 files changed