powerpc/40x: Remove EP405

EP405 is an old type of board based on a 405GP which is obsolete.

Remove it.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/e9534caa51f327c841b3db5f48043a47ad70d246.1590079968.git.christophe.leroy@csgroup.eu