[SVE] Make EVT::getScalarSizeInBits and others consistent with Type::getScalarSizeInBits

An existing function Type::getScalarSizeInBits returns a uint64_t
instead of a TypeSize class because the caller is requesting a
scalar size, which cannot be scalable. This patch makes other
similar functions requesting a scalar size consistent with that,
thereby eliminating more than 1000 implicit TypeSize -> uint64_t
casts.

Differential revision: https://reviews.llvm.org/D87889