arm: Simplify SystemArrayCopy intrinsics.

This applies improvements from
    https://android-review.googlesource.com/2869995
to the arm architecture and generally aligns the code with
with the arm64 version, including a threshold for using the
native (non-intrinsic) implementation.

Also fix the non-primitive array check on arm64.

Test: run-gtests.sh
Test: testrunnerpy --target --32 --optimizing
Change-Id: I2992e5343830142df71ef0d0a08f98973f799c80
2 files changed