sfc: Rename register I/O header and functions used by both Falcon and Siena

While we're at it, use type suffixes of 'd', 'q' and 'o', consistent
with register type names.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>