libmeminfo: add GPU total memory usage query function

Add ReadGpuTotalUsageKb to query GPU total memory usage collected using
BPF program. Modify VTS and unit tests to include new function.

Bug: 171261987
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Change-Id: I79aea5a7cccc30c0a387e4ab814c4e6361ac5c8d
3 files changed