powerpc/bpf: Cleanup bpf_jit.h

- PPC_EX32() is only used by ppc32 JIT. Move it to bpf_jit_comp32.c
- PPC_LI64() is only valid in ppc64. #ifdef it
- PPC_FUNC_ADDR() is not used anymore. Remove it.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/58f5b66b2f8546bbbee620f62103a8e97a63eb7c.1644834730.git.naveen.n.rao@linux.vnet.ibm.com