powerpc/lib/feature-fixups: Use PPC_RAW_xxx() macros

Use PPC_RAW_xxx() macros instead of open coding assembly
opcodes.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
[mpe: Fix bad converison in do_stf_exit_barrier_fixups()]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/e79cd8e111ca13bf8c61a384bac365aa7e207647.1621506159.git.christophe.leroy@csgroup.eu