powerpc/config: Add CONFIG_BOOKE_OR_40x

We have many functionnalities common to 40x and BOOKE, it leads to
many places with #if defined(CONFIG_BOOKE) || defined(CONFIG_40x).

We are going to add a few more with KUAP for booke/40x, so create
a new symbol which is defined when either BOOKE or 40x is defined.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/9a3dbd60924cb25c9f944d3d8205ac5a0d15e229.1634627931.git.christophe.leroy@csgroup.eu