Be nice to CellSPU: for this target getSetCCResultType

Be nice to CellSPU: for this target getSetCCResultType
may return i8, which can result in SELECT nodes for
which the type of the condition is i8, but there are
no patterns for select with i8 condition.  Tweak the
LegalizeTypes logic to avoid this as much as possible.
This isn't a real fix because it is still perfectly
possible to end up with such select nodes - CellSPU
needs to be fixed IMHO.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@57968 91177308-0d34-0410-b5e6-96231b3b80d8