dts: Add _STRING_TOKEN and _STRING_UPPER_TOKEN to string-array

This commit adds string token versions of the values also
in items inside string-array.

Signed-off-by: Radosław Koppel <r.koppel@k-el.com>
Co-authored-by: Marti Bolivar <marti.bolivar@nordicsemi.no>
Co-authored-by: Kumar Gala <galak@kernel.org>