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)
1 file changed