inmates/configs: Pick up PM timer address from Comm Region

inmates/configs: Pick up PM timer address from Comm Region

Instead of probing it, use the information that is now provided via the
Communication Region. This requires to map the region also into the
tiny-demo cell.

We can now drop all explicit port permissions from the inmate's cell
configurations as this is now done automatically by the hypervisor.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>