powerpc/82xx: Remove CONFIG_8260 and CONFIG_8272

CONFIG_8272 is never used, remove it.

CONFIG_8260 is redundant with CONFIG_PPC_82xx, remove it.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/80930252a5167f3cdaa7eb694074d75521a0bdf9.1692259495.git.christophe.leroy@csgroup.eu