sfc: EFX_WORKAROUND_ALWAYS is really specific to Falcon-architecture

The workarounds that currently use EFX_WORKAROUND_ALWAYS are in
Falcon-specific or Falcon-arch-specific code, so get rid of the
conditions altogether.  Add/move comments as appropriate.

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