Make create_reference_dumps.py faster.

Since we now build and install all vndk libraries,regardless of
dependencies, we may just look for all files with the extension '.lsdump' for
TARGET_ARCH and TARGET_2ND_ARCH, and copy them to the given reference dump
directory.

Test: utils/create_reference_dumps.py --version current -ref-dump-dir
      <dir> creates reference dumps at <dir>

Change-Id: Ic9db57b00614b3e8dc18d8e56eab4bd87df1723c