powerpc/kconfig: Restore alphabetic order of the selects under CONFIG_PPC

Commit a7d2475a

 ("powerpc: Sort the selects under CONFIG_PPC")
sorted all selects under CONFIG_PPC.

4 years later, several items have been introduced at wrong place,
a few other have been renamed without moving them to their correct
place.

Reorder them now.

While we are at it, simplify the test for a couple of them:
- PPC_64 && PPC_PSERIES is simplified in PPC_PSERIES
- PPC_64 && PPC_BOOK3S is simplified in PPC_BOOK3S_64

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/361ee3fc5009c709ae0ca592249bb0702c6ef073.1619024780.git.christophe.leroy@csgroup.eu