edk2: Update additional licenses in Readme.md

edk2: Update additional licenses in Readme.md

Update the list of additional licenses in Readme.md.  For additional
licenses from a git submodule, provide a link to the license file
in the remote git repository.  This makes the links in Readme.md
when viewed from the edk2 repository GitHub landing page
https://github.com/tianocore/edk2/ functional from a web browser.

* Remove references EdkCompatibilityPkg
* Update link to OpenSSL to license file in the git submodule link
  to https://github.com/openssl/openssl
* Add link to license file in the git submodule like to
  https://github.com/ucb-bar/berkeley-softfloat-3 for
  ArmSoftFloatLib

Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>