powerpc: remove dead config options for MPC85xx platform support

Commit 384e338a ("powerpc: drop MPC8540_ADS and MPC8560_ADS platform
support") and commit b751ed04 ("powerpc: drop MPC85xx_CDS platform
support") removes the platform support for MPC8540_ADS, MPC8560_ADS and
MPC85xx_CDS in the source tree, but misses to remove the config options in
the Kconfig file. Hence, these three config options are without any effect
since then.

Drop these three dead config options.

Fixes: 384e338a ("powerpc: drop MPC8540_ADS and MPC8560_ADS platform support")
Fixes: b751ed04 ("powerpc: drop MPC85xx_CDS platform support")
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@redhat.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://patch.msgid.link/20240927095203.392365-1-lukas.bulwahn@redhat.com