[platforms/hwcomposer] Include the android-config.h in the hwcomposer_backend

Summary:
This special file[1] can contain the defines like QTI_BSP and QCOM_BSP
which then modifies the API/ABI of the hwcomposer[2].

This defines are required in order to make kwin_wayland work on !nexus
QCOM devices and also possibly other special devices.

[1] https://github.com/Halium/android-headers/blob/master/android-config.h
[2] https://github.com/Halium/android-headers/blob/halium-7.1/hardware/hwcomposer.h#L290

Test Plan: built kwin locally on such device

Reviewers: #kwin, davidedmundson

Reviewed By: davidedmundson

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D7719