CryptoPkg: Adding OpenSSL as one submodule of EDKII repo

CryptoPkg: Adding OpenSSL as one submodule of EDKII repo

A submodule allows to keep another Git repository in a subdirectory
of main repository. The submodule repository has its own history, which
does not interfere with the history of the current repository. This can
be used to have external dependencies such as third party libraries.

After the extra patch for EDKII-OpenSSL build was removed, OpenSSL can
be one typical submodule use case in EDKII project. This patch adds the
openssl git repository into EDKII project as one submodule.

One .gitmodules file will be generated with the submodule info:
    [submodule "CryptoPkg/Library/OpensslLib/openssl"]
            path = CryptoPkg/Library/OpensslLib/openssl
            url = https://github.com/openssl/openssl

The user can use the following command to clone both main EDKII repo and
openssl submodule:
   1) Add the "--recursive" flag to their git clone command:
      $ git clone --recursive https://github.com/tianocore/edk2
or 2) Manually initialize and the submodules after the clone operation:
      $ git clone https://github.com/tianocore/edk2
      $ git submodule update -–init -–recursive

For Pull operations, "git pull" will not update the submodule repository.
So the following combined commands can be used to pull the remote submodule
updates (e.g. Updating to new supported OpenSSL release)
  $ git pull –-recurse-submodules && \
    git submodule update -–recursive --remote

Cc: Ye Ting <ting.ye@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Qin Long <qin.long@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>