[scudo] Use DefaultSizeClassMap for 32-bit

Summary:
With the recent changes to the Secondary, we use less bits for UnusedBytes,
which allows us in return to increase the bits used for Offset. That means
that we can use a Primary SizeClassMap allowing for a larger maximum size.

Reviewers: kcc, alekseyshl

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D27816

llvm-svn: 289838