Previously it would fail, and then we'd fall back to the transfer path
for things like readpix. But it would spam logcat w/ bo_mmap fail
messages. Since gralloc allocated buffers for GPU usage are allocate
without _USE_MAPPABLE, let's just assume we can't map imported bo's.
Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16477>