powerpc: remove unused CONFIG_405EP

All users of Kconfig symbol 405EP were removed in release v2.6.27.
Remove this symbol (and a useless select of it) too.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Acked-by: Josh Boyer <jwboyer@gmail.com>
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>