Use libandroid_runtime lazily

This is a part of cutting dependency from libmediandk to
libandroid_runtime.

By making a libandroid_runtime to be loaded lazily,
libmediandk won't load libandroid_runtime when it is used as a LL-NDK.

Bug: 124268753
Test: m -j
Change-Id: Ib040856c58d38e11a5f32cd5dd5519910573334b