powerpc/85xx: Fix function naming for p1023_rdb platform

p1023_rdb platform is a copy of mpc85xx_rdb platform and some of its
functions have kept mpc85xx_rdb names.

Rename the said functions.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/6cb9865d916231c38401ba34ad1a98c249fae135.1676711562.git.christophe.leroy@csgroup.eu