Does praying two rak'ahs after 'Isha' with the intention of Qiyam al-Layl, while limiting the recitation therein to Surat al-Ikhlas and Surat al-Kawthar, count as Qiyam al-Layl according to Sharia, or is طول (prolongation) a condition for them?

These two rak'ahs are achieved by the very act of performing the night vigil (qiyam al-layl). The more a servant prays at night, the more complete their reward will be. Prayer is the best of deeds, and the best of supererogatory acts are those performed at night, especially in the depths of the night.