platsupport: avoid overriding timeout error

Use a different error when reading the time due to an ETIME and fail if
reading the time returns an error.

platsupport: reset timeout if time has passed

platsupport: clarify loops in local_time_manager

- return early if there is no timeout to set
- or if we're succesful

platsupport: reset current_timeout on set_timeout

- if we call ltimer_set_timeout, it could fail. Reset
timeout to UINT64_MAX before we set the timeout and only set
current timeout if we actually manage to reprogram the timer.

platsupport: fix bug in local time manager

The time manger needs to set a new timeout if the old timeout has
already passed.

libplatsupport: fix arguments to ltimer_set_timeout

platsupport: add time manager + local implementation

This is an interface for time services, plus a default implementation of a local time
manager.

The time manager takes an ltimer and uses it to provide the
current time and timeouts which are called as callbacks. It provides a
mapping between ids (generated by the time manager) and callbacks.

Simply put this time manager interface uses an ltimer and the timeout data
structure to provide local timeout multiplexing.