lib/string_helpers: Consolidate string helpers implementation

There are a few implementations of string helpers in the tree like yesno()
that just returns "yes" or "no" depending on a boolean argument. Those
are helpful to output strings to the user or log.

In order to consolidate them, prefix all of them str_ prefix to make it
clear what they are about and avoid symbol clashes.
Taking the commoon `val ? "yes" : "no"` implementation,  quite a few
users of open coded yesno() could later be converted to the new
function:

$ git grep '?\s*"yes"\s*' | wc -l
286
$ git grep '?\s*"no"\s*' | wc -l
20

The inlined function should keep the const strings local to each
compilation unit, the same way it's now, thus not changing the current
behavior.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/202201260...