Android: drop LLVM support on Lollipop

Mesa no longer supports LLVM 3.5 for any targets we support.
Android-x86 adds support for llvmpipe which could work, but android-x86
for L is using mesa 11.0 anyway.

Dropping this support enables clean-up of libelf dependencies.

Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Chih-Wei Huang <cwhuang@linux.org.tw>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>