Change the default overfetching memcpy preload offset to 128 for Rpi

A preload offset of 128 seems to do better with the current version.
In fact, the non-overfetching variant with preload offset of 96
shows a performance regression, so the currently favored preload
offset of 128 should definitely remain in force.
Re-enable memcpy_armv5te in --all setting in benchmark program
Add checks if CHECK_EARLY_PRELOADS is set for unaligned case.