Add Imagination platform support v2

Finalization of !54 (closed)
Depends on !69 (merged)

External Android.bp file should be created in order to build this module:

cc_library_shared {
    name: "hwcomposer.drm_imagination",
    defaults: ["hwcomposer.drm_defaults"],
    srcs: [":drm_hwcomposer_platformimagination"],
    whole_static_libs: ["drm_hwcomposer"],
    shared_libs: ["libion"],
    include_dirs: [
        "path/to/imgtec/include/files",
    ],
}

Imagination provides different headers that should match their gralloc proprietary binary. These headers are redefine/extending existing HAL_PIXEL_FORMAT_XXXX definitions. Some of them are available publicly: https://android.googlesource.com/platform/hardware/intel/img/hwcomposer/+/refs/heads/master/merrifield/include/pvr/hal/img_gralloc_common_public.h
https://github.com/xen-troops/android_external_drm_hwcomposer/blob/android-9.0.0_r3-xt0.2/img_gralloc_common_public.h