powerpc/64: whitelist unresolved modversions CRCs

These are a symptom of CRC generation failure in generic
build code, and not powerpc specific.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Tested-by: Stephen Rothwell <sfr@canb.auug.org.au>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Fixes: 9445aa1a ("ppc: move exports to definitions")
Signed-off-by: Michal Marek <mmarek@suse.com>