Merging r374164:

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r374164 | atanasyan | 2019-10-09 06:12:21 -0700 (Wed, 09 Oct 2019) | 8 lines

[mips] Split expandLoadImmReal into multiple methods. NFC

The `expandLoadImmReal` handles four different and almost non-overlapping
cases: loading a "single" float immediate into a GPR, loading a "single"
float immediate into a FPR, and the same couple for a "double" float
immediate.

It's better to move each `else if` branch into separate methods.
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