[mips] Use MTHC1 when it is available (MIPS32r2 and later) for both FP32 and FP64
Summary:
To make this work for both AFGR64 and FGR64 register sets, I've had to make the
instruction definition consistent with the white lie (that it reads the lower
32-bits of the register) when they are generated by expandBuildPairF64().
Corrected the definition of hasMips32r2() and hasMips64r2() to include
MIPS32r6 and MIPS64r6.
Depends on D3956
Reviewers: jkolek, zoran.jovanovic, vmedic
Reviewed By: vmedic
Differential Revision: http://reviews.llvm.org/D3957
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210771
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