Additionally check TARGET_IS_64_BIT for binder bitness

Since TARGET_USES_64_BIT_BINDER could be not set, first check
TARGET_IS_64_BIT when determining binder bitness.

Test: lunch aosp_walleye-userdebug && m -j vndk, then check
directory structure
Bug: 111773572

Change-Id: If75d5946b38d7b5bc15798b273e0450035c8c43a