sfc: Rename Falcon-arch filter implementation types and functions

The filter table(s) on EF10 are managed by firmware and will need
almost entirely separate code.  Rename the types and functions used
within the existing implementation.  The current definition of struct
efx_filter_spec is really implementation-specific, so we need to keep
it.  For now, define a separate structure for the internal
representation but leave them identical.
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>