tsan: move AccessType to tsan_defs.h

It will be needed in more functions like ReportRace
(the plan is to pass it through MemoryAccess to ReportRace)
and this move will allow to split the huge tsan_rtl.h into parts
(e.g. move FastState/Shadow definitions to a separate header).

Depends on D107465.

Reviewed By: melver

Differential Revision: https://reviews.llvm.org/D107466