Add csv parser for the power profile library.

There are enough variants of csv, and it's simple enough that
it's easier to just have our own parser than to introduce a
dependency on some other library, as this library will be used
in a variety of environments.

Test: atest frameworks/base/tools/powermodel --host
Change-Id: Ib0f7aceb2a58b58f447f6bcef5c95729303dee8a