[llvm-profgen] Support perf script without parsing MMap events

This change supports to run without parsing MMap binary loading events instead it always assumes binary is loaded at the preferred address. This is used when we have assured no binary load address changes or we have pre-processed the addresses resolution. Warn if there's interior mmap event but without leading mmap events.

Reviewed By: hoy

Differential Revision: https://reviews.llvm.org/D107097