powerpc/inst: Remove PPC_INST_BL

Convert last users of PPC_INST_BL to PPC_RAW_BL()

And remove PPC_INST_BL.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/d9eacb758e7ae7cf224211ebe3f6f7d409a333be.1652074503.git.christophe.leroy@csgroup.eu