[x32] Fix FrameIndex check in SelectLEA64_32Addr

Summary:
Fixes http://llvm.org/bugs/show_bug.cgi?id=20016 reproducible on new
lea-5.ll case.
Also use RSP/RBP for x32 lea to save 1 byte used for 0x67 prefix in
ESP/EBP case.

Test Plan: lea tests modified to include x32/nacl and new test added

Reviewers: nadav, dschuff, t.p.northover

Subscribers: llvm-commits, zinovy.nis

Differential Revision: http://reviews.llvm.org/D4929