ci: update prebuilts to qemu7.1.0

Update prebuilts submodule refreshing the x86 qemu prebuilt binary and
introducing the aarch64 qemu prebuilt binary.

Note: the qemu machine is forced to virt-6.2 to prevent enabling the
FEAT_LPA2 feature. The reason is the use in the Hafnium CI of linux
kernel 5.10 which has a bug preventing it to boot properly when
FEAT_LPA2 is implemented [1].

[1] https://github.com/qemu/qemu/commit/0942820408dc788560f6968e9b5f011803b846c2

Change-Id: I1aca0140bcbc0fe8d053c673e9df9547cd51a36a
Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
diff --git a/test/hftest/hftest.py b/test/hftest/hftest.py
index 96b49ae..e27a064 100755
--- a/test/hftest/hftest.py
+++ b/test/hftest/hftest.py
@@ -229,7 +229,7 @@
         exec_args = [
             "timeout", "--foreground", time_limit,
             QEMU_PREBUILTS,
-            "-no-reboot", "-machine", "virt,virtualization=on,gic-version=3",
+            "-no-reboot", "-machine", "virt-6.2,virtualization=on,gic-version=3",
             "-cpu", cpu, "-smp", "8", "-m", "1G",
             "-nographic", "-nodefaults", "-serial", "stdio",
             "-d", "unimp", "-kernel", os.path.abspath(self.args.hypervisor),