[SVE] Replace TypeSize comparison operators in llvm/utils/TableGen

In CodeGenDAGPatterns.cpp we were relying upon TypeSize comparison
operators for ordering types, when we can actually just use the known
minimum size since the scalable property is already being taken into
account. Also, in TypeInfer::EnforceSameSize I fixed some implicit
TypeSize->uint64_t casts by changing the code to test the equality
of TypeSize objects instead.

In other places I have replaced calls to getSizeInBits() with
getFixedSizeInBits() because we are only ever expecting integer values.

Differential Revision: https://reviews.llvm.org/D88947