tests: kernel: timer_api: enabling test-suite for Qemu Cortex-M0

After the Qemu Cortex-M0 timer driver rework, we may
enable the test-suite that had been (always) excluded
from running on this platform.

Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>