Set `TARGET_USES_64_BIT_BINDER` for mainline_sdk.

Devices are all using 64 bit binder, and mainline_sdk should too.
According the comment here: https://cs.android.com/android/platform/superproject/+/master:build/make/target/board/BoardConfigMainlineCommon.mk;l=25;drc=6e7693f1597a0934833a72faf35e918dfbdb6ecd,
this flag is required even for non-64 bit devices.

`libbinder` doesn't compile on host with 32 bit binder.

Test: packages/modules/common/build/mainline_modules_sdks.sh \
        --build-platform-sdks-for-mainline --build-release=latest
Change-Id: I357ce42e88ad13ed259d573b9dd2bbfc27b82687