Move definition of dist-for-goals before call.

New changes to Soong allow for dist-for-goals to be directly invoked
through the Soong-side of the build system.

This presents a problem, as the dist-for-goals propagation for Soong
lands in make_vars-$(target).mk, which is called before dist-for-goals
is defined.

We move the dist-for-goals definition (through moving where distdir.mk
is included) to be before any possible use of the call to
dist-for-goals.

Test: m checkbuild
Change-Id: Icef27a4d2239948b07354c87b58c9985a66a53bd