vp9-rtc: Extract content dependency in cyclic refresh

vp9-rtc: Extract content dependency in cyclic refresh

For usage in the external RC. When content_mode = 0,
the cyclic refresh has no dependency on the content
(motion, spatial variance, motion vectors, etc,).

The content_mode = 0, when compared to content_mode = 1,
on rtc set for speed 7: has some regression on some
clips (~3-5%), but overall/average bdrate loss is
about ~1-2%.

Comparing aq_mode=3 with content_mode = 0, vs aq_mode=3:
about ~14% avg/overall bdrate gain, but has ~3-7% regression
on some hard motion clip (e.g.m street).

Change-Id: I93117fabb8f7f89032c15baf1292b201e8c07362