Break MFQE code into it's own file.

It is currently only valid for 16x16 and 8x8 Y blocks. It also filters
4x4 U/V blocks.

Refactor filtering and add associated assembly. Limited test cases show
--mfqe introduces a penalty of ~20% with HD content. The assembly
reduces the penalty to ~15%

Change-Id: I4b8de6b5cdff5413037de5b6c42f437033ee55bf