BaseTools/PatchCheck: Disable text conversion in 'git show'

BaseTools/PatchCheck: Disable text conversion in 'git show'

https://bugzilla.tianocore.org/show_bug.cgi?id=2044

'git show' is used to extract the patch contents for analysis.
Add the flag '--no-textconv' to the 'git show' command to
disable the conversion from some binary file types to text
content.

Without this change, binary files such as .pdf files are
converted to text in the show command and PatchCheck complains
that the wrong line endings are used in the patch.

Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>