powerpc/epapr: Don't use wrteei on non booke

wrteei is only for booke. Use the standard mfmsr/ori/mtmsr
when non booke.

Reported-by: Jan-Benedict Glaw <jbglaw@lug-owl.de>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/b29c7f1727433b003eae050e44072741c8ac223b.1671475543.git.christophe.leroy@csgroup.eu