powerpc/476: define specific cpu table entry for DD1 and DD1.1 cores

From: Benjamin Herrenschmidt <benh@kernel.crashing.org>

There are still some unstable bits on the DD1 and DD1.1 cores. Don't use
the FPU or the tlbivax operation. Define CPU_FTR_476_DD1 and
CPU_FTR_476_DD1_1 for additional workarounds in later patches.

The DD1 core requires workarounds triggered by both CPU_FTR_476_DD1
and CPU_FTR_476_DD1_1. the DD1.1 core only needs CPU_FTR_476_DD1_1
defined.

Isn't the policy generally not to commit workarounds for early/errataful hardware which will not be seen in the real world? Otherwise, every new half-broken core could burn a bunch of feature bits...

-Hollis