BaseTools: add repo name option to SetupGit.py

BaseTools: add repo name option to SetupGit.py

Allow users who didn't clone one of the TianoCore repos from a
canonical URL to specify the name of the repo (edk2, edk2-platforms
or edk2-non-osi) when running SetupGit.py to allow them to configure
their repo properly.

The new option is:

  -n repo, --name repo  set the repo name to configure for, if not
                        detected automatically

Signed-off-by: Rebecca Cran <rebecca@bsdio.com>
Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>
Reviewed-by: Leif Lindholm <leif@nuviainc.com>