Currently, getDmabufId() is placed at C2VdqBqBlockPool.h. However,
the header file already has many dependencies. The caller of
getDmabufId() would need to add many unnecessary dependency libraries.

This CL splits the method to a dedicated file to reduce this issue.

Bug: 205501954
Test: m -j32

Change-Id: Ie7e366ddf77ceec105cbacf6d16e6b6dc3a58198