Fix sub-operand size mismatch in tocentry operands.

The tocentry operand class refers to 64-bit values (it is only used in 64-bit,
where iPTR is a 64-bit type), but its sole suboperand is designated as 32-bit
type.  This causes a mismatch to be detected at compile-time with the TableGen
patch I'll check in shortly.

To fix this, this commit changes the suboperand to a 64-bit type as well.

llvm-svn: 177427