hftest: use a faster pauth algorithm for cpu max

Default qemu cpu max enables an architected pauth algorithm.
Using a faster (but cryptographically weaker) impdef algorithm
for cpu max gains a lot on performance, particularly for the
linux boot tests.

Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Change-Id: Icd2f4e9e81524219dfd587de0d8b47188f23be24
diff --git a/test/hftest/hftest.py b/test/hftest/hftest.py
index 03daf98..22ca699 100755
--- a/test/hftest/hftest.py
+++ b/test/hftest/hftest.py
@@ -57,6 +57,8 @@
 
 VM_NODE_REGEX = "vm[1-9]"
 
+QEMU_CPU_MAX = "max,pauth-impdef=true"
+
 def read_file(path):
     with open(path, "r") as f:
         return f.read()
@@ -225,7 +227,11 @@
         time_limit = "120s" if is_long_running else "10s"
         # If no CPU configuration is selected, then test against the maximum
         # configuration, "max", supported by QEMU.
-        cpu = self.args.cpu or "max"
+        if not self.args.cpu or self.args.cpu == "max":
+            cpu = QEMU_CPU_MAX
+        else:
+            cpu = self.args.cpu
+
         exec_args = [
             "timeout", "--foreground", time_limit,
             QEMU_PREBUILTS,