powerpc/optprobes: use PPC_RAW_ macros

Use PPC_RAW_ macros to simplify the code.

And use PPC_LO/PPC_HI instead of IMM_L/IMM_H which are for
internal use inside ppc-opcode.h

Those macros are self explanatory, comments can go as well.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/5a167b8ba4d33a5c09cd504f0c862e25ffe85459.1621516826.git.christophe.leroy@csgroup.eu