timer: sandbox: work without device tree

timer: sandbox: work without device tree

A default invocation of sandbox U-Boot apparently uses no device tree,
which means that no timer is registers, which in turn means that the
sleep shell command hangs.

Fix the sandbox timer code to register a device when there's no DT, just
like e.g. the sandbox reset driver does. When there's no DT, the DM uclass
can't initialize clock_rate from DT, so set a default value in the
timer code instead.

Signed-off-by: Stephen Warren <[email protected]>
Reviewed-by: Bin Meng <[email protected]>
Acked-by: Simon Glass <[email protected]>