qemu: Default to TPM 2.0 for ARM virt guests

qemu: Default to TPM 2.0 for ARM virt guests

The TPM 2.0 specification predates ARM virtualization, and so
implementing TPM 1.2 support on ARM was not considered a useful
endeavor.

This is technically a breaking change, but TPM support on ARM was
only introduced fairly recently (libvirt 7.1.0) and the previous
default resulted in non working TPM devices; anyone who has a
working configuration is not going to be affected.

https://bugzilla.redhat.com/show_bug.cgi?id=1970310

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Tested-by: Liu Yiding <liuyd.fnst@fujitsu.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>