lib/string_helpers: Introduce parse_int_array_user()

Merge series from Cezary Rojewski <cezary.rojewski@intel.com>:

Continuation of recent upstream discussion [1] regarding user string
tokenization.

First, parse_int_array_user() is introduced to allow for splitting
specified user string into a sequence of integers. Makes use of
get_options() internally so the parsing logic is not duplicated.

With that done, redundant parts of the sound driver are removed.

Originally similar functionality was added for the SOF sound driver. As
more users are on the horizon, it is desirable to update existing
string_helpers code and provide a unified solution.