etnaviv: fix BO cache to properly work with different flags

Currently if the oldest BO in a bucket has different flags than what we
look for we'll miss the cache.Fix this by iterating over the cached BOs
until we find the oldest one with matching flags. This improves the hit
ratio for some of the buckets.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>