Loop restoration filter

Loop restoration filter

Current implementation is a bilateral filter whose
parameters are transmitted in the bitstream.

derflr: -0.647% BDRATE
hevcmr: -0.794% BDRATE

This is a prelimary patch. Various other variations are to
be investigated next, that will hopefully be less expensive
on the decoder side.

Change-Id: I50634ae8f5014ad0bf7432306348908a349d81e1