The OpActions array had a limit of 32 value types, so change it to use
MVT::MAX_ALLOWED_VALUETYPE in its declaration and change the accesses to
this array to work with a VT.getSimpleVT() that is larger than 32.
Also, add a comment to the place where MVT::MAX_ALLOWED_VALUETYPE is
defined indicating that it must be a multiple of 32.
This is part of the work allow MVT::LAST_VALUETYPE be greater than 32.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@74130 91177308-0d34-0410-b5e6-96231b3b80d8