arch-gcn3,python: Upgrade gpu_isa_parser.py to Python3

Change-Id: I0a37809589d3796f7c74614a337cc690aae6c9a0
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/47021
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Reviewed-by: Matthew Poremba <matthew.poremba@amd.com>
Maintainer: Matt Sinclair <mattdsinclair@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/arch/amdgpu/gcn3/gpu_isa_parser.py

@@ -1245,9 +1245,9 @@ class GpuIsaParser(Grammar):
     # error rule
     def p_error(self, t):
         if t:
-            print '%d: syntax error at "%s"' % (t.lexer.lineno, t.value)
+            print('%d: syntax error at "%s"' % (t.lexer.lineno, t.value))
         else:
-            print 'unknown syntax error'
+            print('unknown syntax error')
         import pdb; pdb.set_trace()
 
     # end rules