powerpc/ppc-opcode: Define and use PPC_RAW_SETB()

We have PPC_INST_SETB then build the 'setb' instruction in the
user.

Instead, define PPC_RAW_SETB() and use it.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/b08a4f26919a8f8cdcf7544ab552d9c1c63418b5.1657205708.git.christophe.leroy@csgroup.eu