arch-hsail: changed gen.py shebang from python(3) to python2.7

gen.py includes code_formatter from m5.util. code_formatter uses the
python2 __metaclass__ attribute, which is ignored by python3, causing
the code_formatter.pattern attribute to be unset.

This prevented scons from building against HSAIL_X86

Signed-off-by: Ryan Gambord
<gambordr@oregonstate.edu>

Change-Id: I5a8bf9e730fd629eb7f9a7ac2dce928235a0dae4
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17008
Reviewed-by: Andrea Mondelli <Andrea.Mondelli@ucf.edu>
Reviewed-by: Anthony Gutierrez <anthony.gutierrez@amd.com>
Maintainer: Anthony Gutierrez <anthony.gutierrez@amd.com>
diff --git a/src/arch/hsail/gen.py b/src/arch/hsail/gen.py
index 23ce02e..8dcc92c 100755
--- a/src/arch/hsail/gen.py
+++ b/src/arch/hsail/gen.py
@@ -1,6 +1,4 @@
-#! /usr/bin/python
-
-#
+#!/usr/bin/env python2.7
 #  Copyright (c) 2015 Advanced Micro Devices, Inc.
 #  All rights reserved.
 #