acpica: update to 20150515 and fix conflicts with other layers

Meta-virtualization and meta-luv both has iasl_*.bb, which is a subset of this recipe. Extend this recipe to provide the native tools and add the necessary runtime conflict options.

Also address style issues by moving around a few bits and adding some whitespace.

Signed-off-by: Koen Kooi <koen.kooi@linaro.org>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>