Revert "Emit the SubRegTable with the smallest possible integer type."

This reverts commit 151760.

We want to move getSubReg() from TargetRegisterInfo into MCRegisterInfo,
but to do that, the type of the lookup table needs to be the same for
all targets.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151814 91177308-0d34-0410-b5e6-96231b3b80d8