Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Use TRex release v2.41 to support both x86 and aarch64"
  - Use TRex release v2.41 to support both x86 and aarch64

    Currently Yardstick uses Cisco's TRex release v2.28 which
    can only support x86, for the consideration of
    multi-arch support of Yardstick, the trex release v2.41
    is now available and it can support multi-arch(both x86
    and aarch64) now.

    For the external lib of v2.41, for x86_64, it looks like:
    external_libs/pyzmq-14.5.0/python2/intel/ucs4/64bit/zmq
    for arm64, it looks like:
    external_libs/pyzmq-14.5.0/python2/arm/ucs4/64bit/zmq
    So replace the trex release v2.28 with v2.41.

    JIRA: YARDSTICK-1191

    Change-Id: I22dc3499283d48a89da1145cc480fd7d2a93a1cc
    Signed-off-by: trevortao <trevor.tao@arm.com>