Add entry for ppc64le in arch list

Add entry for ppc64le in arch list

A few tests fails in ppc64le with error:

========
parse error: expected 'probe', 'global', 'function', or '%{'^M
         saw: identifier 'ERROR' at <input>:22:43^M
      source:     %( arch == "ppc64le"            %? %: ERROR %)^M
                                                        ^^M
^M
1 parse error.^M
Pass 1: parse failed.  [man error::pass1]^M
FAIL: preprocessor basic ops
=========

This is because ppc64le is not added to arch list in systemtap.exp .
cmd_parse.exp also fails with similar error for arch.  Modifying the
code for ppc64le.

Signed-off-by: Athira Rajeev <atrajeev@in.ibm.com>