powerpc/opcodes: Remove unused PPC_INST_XXX macros

The following PPC_INST_XXX macros are not used anymore
outside ppc-opcode.h:
	- PPC_INST_LD
	- PPC_INST_STD
	- PPC_INST_ADDIS
	- PPC_INST_ADD
	- PPC_INST_DIVD

Remove them.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/8c28636126f69141419953b5638b4a908c184dc1.1652074503.git.christophe.leroy@csgroup.eu