arm64: timer: Add TVAL timeout IRQ trigger test

So far we were only testing the CVAL register. Add a test which programs
a (relative) TVAL value to check this functionality as well.
Also we go into WFI and wait for the interrupt to release us from it.
The timer tests are run with a 2 second timeout on the host side, so
that any failure in coming back would be covered.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Andrew Jones <drjones@redhat.com>