Enable kernel XZ compression option on BOOK3S_32. Tested on G4
PowerBook.
Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
[mpe: Use one select under the PPC symbol guarded by if PPC_BOOK3S]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>