[platforms/hwcomposer] Include the android-config.h in the hwcomposer_backend
This special file can contain the defines like QTI_BSP and QCOM_BSP
which then modifies the API/ABI of the hwcomposer.
This defines are required in order to make kwin_wayland work on !nexus
QCOM devices and also possibly other special devices.
Test Plan: built kwin locally on such device
Reviewers: KWin, davidedmundson
Reviewed By: davidedmundson
Differential Revision: https://phabricator.kde.org/D7719