[compiler-rt] [dfsan] Unify aarch64 mapping
This patch reorganize the platform specific mapping information to
export the application mask on a external variable. This exported
variable will be used by intrumentation phase to create code to be
used on architecture with multiple VMA range.
The patch creates a new header, dfsan_platform.h, and move all the
mapping information and also create function accessors to the
Also for aarch64 it initialize application exported mask to the
value based on runtime VMA detection.