android: utils: load SurfaceTexture constructors

init_z needs API 26 and is the most suitable since it allows creating
SurfaceTexture in a detached state, while init_iz needs API 19 and
cannot be created without an EGL context currently bounded.

init_i is the most compatible version (API 11) but won't allow
single-buffering.

Signed-off-by: Alexandre Janniaux <ajanni@videolabs.io>