zink: make general bo allocation more robust by iterating

zink: make general bo allocation more robust by iterating

previously there was a fallback path here (broken by f6d3a5755f6)
which would attempt to demote BAR allocations to other heaps on failure
to avoid oom

this was great, but it's not the most robust solution, which is to iterate
all the memory types matching the given heap and try them in addition to having
a demotion fallback

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22479>