[mips] Fix more incorrect uses of HasMips64 and isMips64()

Summary:
- Conditional moves acting on 64-bit GPR's should require MIPS-IV rather than MIPS64
- ISD::MUL, and ISD::MULH[US] should be lowered on all 64-bit ISA's

Patch by David Chisnall
His work was sponsored by: DARPA, AFRL

I've added additional testcases to cover as much of the codegen changes
affecting MIPS-IV as I can. Where I've been unable to find an existing
MIPS64 testcase that can be re-used for MIPS-IV (mainly tests covering
ISD::GlobalAddress and similar), I at least agree that MIPS-IV should
behave like MIPS64. Further testcases that are fixed by this patch will follow
in my next commit. The testcases from that commit that fail for MIPS-IV without
this patch are:
    LLVM :: CodeGen/Mips/2010-07-20-Switch.ll
    LLVM :: CodeGen/Mips/cmov.ll
    LLVM :: CodeGen/Mips/eh-dwarf-cfa.ll
    LLVM :: CodeGen/Mips/largeimmprinting.ll
    LLVM :: CodeGen/Mips/longbranch.ll
    LLVM :: CodeGen/Mips/mips64-f128.ll
    LLVM :: CodeGen/Mips/mips64directive.ll
    LLVM :: CodeGen/Mips/mips64ext.ll
    LLVM :: CodeGen/Mips/mips64fpldst.ll
    LLVM :: CodeGen/Mips/mips64intldst.ll
    LLVM :: CodeGen/Mips/mips64load-store-left-right.ll
    LLVM :: CodeGen/Mips/sint-fp-store_pattern.ll

Reviewers: dsanders

Reviewed By: dsanders

CC: matheusalmeida

Differential Revision: http://reviews.llvm.org/D3343

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206183 91177308-0d34-0410-b5e6-96231b3b80d8