winsys/radeon: Use a single buffer cache manager again

winsys/radeon: Use a single buffer cache manager again

The trick is to generate a unique buffer usage value for each possible
combination of domains and flags, with only one bit set each for the
domains and flags. This ensures pb_check_usage() only returns TRUE when
the domains and flags the cached buffer was created for exactly match
the requested ones.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>