yocto/systemd: Disable background services

15 simulation minutes after boot, a systemd timer launches a service to
clean up any temporary files. Disable this timer to prevent interference
with HIPC testing.

systemd-timesync periodically wakes up to synchronize the system clock
with the network, disrupting testing. Additionally, the simulated clock
does not advance at real-time so it is ineffective in the model.

Introduce a recipe to disable these service for all Kronos
architectures.

Signed-off-by: Peter Hoyes <Peter.Hoyes@arm.com>