C2VdaBqBlockPool: support surface switch at protected playback

Originally, protected buffer allocator has restriction that we can
only call priorGraphicAllocation() method once for each buffer. But we
have to call priorGraphicAllocation() again when switching surface. So
surface switching is not supported at protected playback.

However, the restriction is relaxed at ag/13461483. This CL removes
the protected playback check at surface switching.

Bug: 160110407
Test: m -j32

Change-Id: I21154fa9a9f69db1e2eee89f296daae8932239d1