iris: Fix aux assertion in resource_get_handle

iris_resource_get_handle currently asserts that the resource has an aux state that is suitable for sharing. However, the caller of this function can pass a flag to specify that it will handle flushing/resolving the resource as needed for sharing. Take this flag into account when asserting the state of the aux buffer.

• Fixes: 95589652 ("iris: Skip resolve if there's no context.")
• Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111150
• Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111162

/cc @rantogno