[scudo] Avoid splitting aligned allocations on Trusty (#69281)

Don't use multiple tagged pages at the beginning of an allocation, since
it prevents using such allocations for memrefs, and mappings aren't
reused anyway since Trusty uses MapAllocatorNoCache.
Upstreamed from https://r.android.com/2537251

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Co-authored-by: Marco Nelissen <marcone@google.com>