sfc: Refactor efx_mcdi_rpc_start() and efx_mcdi_copyin()
sfc: Refactor efx_mcdi_rpc_start() and efx_mcdi_copyin()

Preparation for asynchronous MCDI requests.

Signed-off-by: Ben Hutchings <0672176982fbc629cc374f31a7a45ae1671abf90@solarflare.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs