EDAC: Drop obsolete PPC4xx driver

Since

  47d13a26 ("powerpc/40x: Remove 40x platforms.")

support for PPC40x platforms has been removed. While the EDAC driver also
mentions PPC440 and PPC460 processors, the driver refuses to probe on anything
other than PPC405. It's unlikely support will ever be added at this point for
these other old platforms, so the driver can be removed.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Link: https://lore.kernel.org/r/20240904192224.3060307-2-robh@kernel.org