Document that quantized PAD behavior is undefined before 1.2 Fix: 122243484 Test: runtime/test/specs/V1_2/pad_quant8.mod.py Change-Id: I1fb9cd46b401109b38879a40d94dc1d3ecf5a39f Merged-In: I1fb9cd46b401109b38879a40d94dc1d3ecf5a39f (cherry picked from commit 3337b5b5b58ee70d1b4c7d2a37e75bac389529b7)