Add embed::poll_for(timer&, timeout, poll_function)

[kammce]

Provides a utility that polls a function for a duration of time and if that time is exceeded, then the function returns and error, otherwise it return success. In this case, an atomic variable is used to detect if the time has been exceeded. The atomic variable is set to 0. embed::timer would schedule itself with a function that flips an atomic flag to a value, lets say 1. If the poll function does not finish before the atomic flag is set to 1, then return with an error. Otherwise return success.

[kammce]

Obsolete by libhal/libhal-util#23