fix(sptool): operators "is/is not" in sp_mk_gen.py

Replace the "is/is not" operator by "==/!=" for literals, to fix the
syntax warnings below:

tools/sptool/sp_mk_generator.py:93: SyntaxWarning: "is not" with a literal. Did you mean "!="?
  return len(sppkg_rule) is not 0

tools/sptool/sp_mk_generator.py:203: SyntaxWarning: "is" with a literal. Did you mean "=="?
  assert(len(uuid_lines) is 1)

Signed-off-by: J-Alves <joao.alves@arm.com>
Change-Id: I10800f6b607942542aa2cbaaecac86b854f6b56a
diff --git a/tools/sptool/sp_mk_generator.py b/tools/sptool/sp_mk_generator.py
index c0beb65..f3af584 100644
--- a/tools/sptool/sp_mk_generator.py
+++ b/tools/sptool/sp_mk_generator.py
@@ -90,7 +90,7 @@
 def is_line_in_sp_gen(line, args :dict):
     with open(args["sp_gen_mk"], "r") as f:
         sppkg_rule = [l for l in f if line in l]
-    return len(sppkg_rule) is not 0
+    return len(sppkg_rule) != 0
 
 def get_file_from_layout(node):
     ''' Helper to fetch a file path from sp_layout.json. '''
@@ -200,7 +200,7 @@
     else:
         with open(get_sp_manifest_full_path(sp_layout[sp], args), "r") as pm_f:
             uuid_lines = [l for l in pm_f if 'uuid' in l]
-        assert(len(uuid_lines) is 1)
+        assert(len(uuid_lines) == 1)
         # The uuid field in SP manifest is the little endian representation
         # mapped to arguments as described in SMCCC section 5.3.
         # Convert each unsigned integer value to a big endian representation