[mips] Split SelectAddr, which was used to match address patterns, into two

[mips] Split SelectAddr, which was used to match address patterns, into two
functions. Set AddedComplexity to determine the order in which patterns are
matched.

This simplifies selection of floating point loads/stores.

No functionality change intended.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175300 91177308-0d34-0410-b5e6-96231b3b80d8