powerpc: Remove Xilinx PPC405/PPC440 support

The latest Xilinx design tools called ISE and EDK has been released in
October 2013. New tool doesn't support any PPC405/PPC440 new designs.
These platforms are no longer supported and tested.

PowerPC 405/440 port is orphan from 2013 by
commit cdeb8994 ("MAINTAINERS: Fix incorrect status tag") and
commit 19624236 ("MAINTAINERS: Update Grant's email address and maintainership")
that's why it is time to remove the support fot these platforms.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/8c593895e2cb57d232d85ce4d8c3a1aa7f0869cc.1590079968.git.christophe.leroy@csgroup.eu