Move aom_util cmake commands to aom_util/aom_util.cmake.

Also adds CONFIG_BITSTREAM_DEBUG support (because it was in
aom_util/aom_util.mk, and that's partly the guidance here).

BUG=https://bugs.chromium.org/p/aomedia/issues/detail?id=76

Change-Id: I971b4025e345fd7d6d766526059f74d8b6ff2ebd
2 files changed