Automaking giant General Motors has moved to shield its subprime lending shop from the impact of a potentially disastrous credit downgrade. Earlier this month, GM transferred ownership of its Residential Funding and GMAC Mortgage units to a newly-formed holding company, Residential Capital Corp, or RESCAP. GMAC provided $2 billion in funding to the venture, which it said will provide “additional operational and financial flexibility” to enhance RFC’s liquidity. GM said that it has no…