[X86] Add phony registers for high halves of regs with low halves

Add registers still missing after r328016 (D43353):
- for bits 15-8  of SI, DI, BP, SP (*H), and R8-R15 (*BH),
- for bits 31-16 of R8-R15 (*WH).

Thanks to Craig Topper for pointing it out.

llvm-svn: 336134