Tune the memcpy for krait.

Streamline the memcpy a bit removing some unnecessary instructions.

The biggest speed improvement comes from changing the size of
the preload. On krait, the sweet spot for the preload in the main
loop is twice the L1 cache line size.

In most cases, these small tweaks yield > 1000MB/s speed ups. As
the size of the memcpy approaches about 1MB, the speed improvement

Change-Id: Ief79694d65324e2db41bee4707dae19b8c24be62
1 file changed