powerpc: Remove CONFIG_PCI_8260

CONFIG_PCI_8260 is not used anymore, remove it.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/19a4c07466ce8b80f287a06eadcc80c4ab1d2c9e.1691474658.git.christophe.leroy@csgroup.eu