core/jni/android/graphics: Cache copy of pre-scaled Bitmaps

Caching some pre-scaled Bitmap objects allows for optimizing later
scaling operations to reduce memory pressure.

CRs-fixed: 451681

Change-Id: Id4341e75911074ff9f565b2d386ccad8f3a223e8
Vectorize bitmap operations on A15 too

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

Change-Id: I1f733f5311376deb78782931ea2b83a8d12c2171