Pass the TPM file descriptor to QEMU via command line.
Instead of passing /dev/tpm0 we now pass /dev/fdset/10 and the additional
parameters -add-fd set=10,fd=20.

This addresses the use case when QEMU is started with non-root privileges
and QEMU cannot open /dev/tpm0 for example.
Signed-off-by: NStefan Berger <stefanb@linux.vnet.ibm.com>