[POWERPC] pasemi: Broaden specific references to 1682M

There will be more product numbers in the future than just PA6T-1682M,
but they will share much of the features. Remove some of the explicit
references and compatibility checks with 1682M, and replace most of them
with the more generic term "PWRficient".

Signed-off-by: Olof Johansson <olof@lixom.net>
Acked-by: Michael Buesch <mb@bu3sch.de>
Acked-by: Doug Thompson <dougthompson@xmission.com>