BoardConfig: Add HTC RGBA offset flag.

FOre use with this commit:

https://github.com/Team-Hydra/android_hardware_qcom_display-legacy/commit/e2d3fae4825f0b1ca2a5ff8ad4cdd9601407cbca

Change-Id: I178ebee610d1439afe8acffb73eb676ec0a2428b