[mips] Provide additional DSP bitconvert patterns

Previously, v2i16 -> f32 bitcast could not be matched.
Add patterns to support matching this and similar types of bitcasts.

Differential revision: https://reviews.llvm.org/D40959


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@320562 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed