ibm-ethernet: delete stale MCA and duplicate PSERIES dependency

MCA support has been removed but this dependency escaped removal.
Also, there is a duplicate PPC_PSERIES dependency that appeared
when the ethernet drivers were separated into vendor/model
specific directories, so we remove that here as well.

Reported-by: Robert de Rooy <robert.de.rooy@gmail.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>