Migrate to using the semi-opaque type rman_res_t to specify rman resources. For now, this is still compatible with u_long.
This is step one in migrating rman to use uintmax_t for resources instead of
Going forward, this could feasibly be used to specify architecture-specific definitions of resource ranges, rather than baking a specific integer type into the API.
This change has been broken out to facilitate MFC'ing drivers back to 10 without