nmk: Use ppc64 for PowerPC 64 bits architecture
nmk: Use ppc64 for PowerPC 64 bits architecture

This is usual to reference PowerPC 64 bits architectures as 'ppc64',
and let 'powerpc' define PowerPC 32 bits ones.

Acked-by: Cyrill Gorcunov <7a1ea01eee6961eb1e372e3508c2670446d086f4@gmail.com>
Signed-off-by: Laurent Dufour <a59ffce977ae3d39bdc87f81ff88b229ad58db88@linux.vnet.ibm.com>
Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@virtuozzo.com>

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