Collapse code paths for single- and multi-input kernels.

This patch simplifies the RenderScript JNI layer by replacing six functions
with a single funciton.  This new function now handles all previous cases.
Functions in android.renderscript.script have been updated to use this new JNI
function.

Change-Id: I77e4b155cc7ca1581b05bf901c70ae53a9ff0b12