powerpc: Remove 40x leftovers

Remove stale references to 40x.

Fixes: e939da89 ("powerpc: Remove 40x from Kconfig and defconfig")
Fixes: 548f5244 ("powerpc/40x: Remove EP405")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/ab30ae302783d8617d407864b92db1b926ab5ab9.1720694914.git.christophe.leroy@csgroup.eu