frameworks/base: vectorize Bitmap operations

Enable gcc vectorizing optimizations for Bitmap operations within
libandroid_runtime.so.  Adds -ftree-vectorize -mvectorize-with-neon-quad
-fprefetch-loop-arrays to functions and compiles Bitmap.cpp in ARM mode
(necessary to enable vectorizing optimizations) for appropriate targets.

Change-Id: I12defef6f47adf41af849df6e750097f5906d92d
Vectorize bitmap operations on A15 too

 * Commit a2e20761b5ad646ce3f08ed24995799dd81acee0 enables GCC
   vectorization for bitmap operations on Krait. Enable it on A15 also.

Change-Id: I1f733f5311376deb78782931ea2b83a8d12c2171