Loosen restriction on F16 surfaces - allow "legacy" F16 mode

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4231

Change-Id: I032cdf82468ca11639760eb99773a88a5808ebe6
Reviewed-on: https://skia-review.googlesource.com/4231
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
3 files changed