powerpc/85xx: Fix description of MPC85xx and P1/P2 boards options

More MPC85xx and P1/P2 boards options have incorrect description. Fix them
to include list of all boards for which they enable/disable support.

Signed-off-by: Pali Rohár <pali@kernel.org>
Acked-by: Scott Wood <oss@buserror.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220709124305.17559-1-pali@kernel.org