libhybris: replace 7.1-caf pkg with separate test_hwcomposer binary

As observed on UBPorts, hwcomposer implementation on Android 7 CAF (non-Nexus Qualcomm) devices has slight differences in employed structs, which makes them binary incompatible with AOSP headers.

Halium 7.1 android-headers extracted from LineageOS include those modifications (e. g. https://github.com/Halium/android-headers/blob/halium-7.1/hardware/hwcomposer.h#L290), so it is enough to add QTI_BSP/QCOM_BSP to defines of programs utilizing those headers. In case of libhybris, only test_hwcomposer is affected so far on 7.1 (might be not true for Android 5.1/6!).

This change avoids providing libhybris-7.1-caf package by building a separate binary of test_hwcomposer for affected devices.