powerpc/inst: Remove PPC_INST_BRANCH

Convert last users of PPC_INST_BRANCH to PPC_RAW_BRANCH()

And remove PPC_INST_BRANCH.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/fa8807108a2ef2287a2c9651d6e1ff7c051923d9.1652074503.git.christophe.leroy@csgroup.eu