GPU Memory: install gpu_mem.o and integrate libgpumem

This change integrates libgpumem into gpuservice. gpu_mem.o c program is
required in the blueprint so that gpu_mem.o will be compiled and
installed at /system/etc/bpf/.

This change also adds a proper CleanSpec.mk for gpu_mem.o

Bug: 154524735
Test: adb shell dumpsys gpu --gpumem
Change-Id: Iad09d061691ffd4cf0fc4bde63cb6f0ae459aa27
Merged-In: Iad09d061691ffd4cf0fc4bde63cb6f0ae459aa27