Allow OVERLAY frames to use the show_exsiting_frame flag

ARF with zero strength temporal filter can be reused by setting the
show_existing_frame = 1, and in this case, there is no need to
refresh the reference frame buffer. However, we used the flag
"refresh_golden_frame" as the identifier for the starting point of a gf
group.

A new flags "is_arf_filter_off" is used to record if the filter with
strengrh zero is used.

Change-Id: I25971a760f6e1638d5147fe30488c48125512b1a