Instead of having CLPF write to an entire new frame and
copy the result back into the original frame, make the
filter able to work in-place by keeping a buffer of size
frame_width*filter_block_size and delay the write-back
by one filter_block_size row.

This reduces the cycles spent in the filter to ~75%.

Change-Id: I78ca74380c45492daa8935d08d766851edb5fbc1