[sanitizer] Add GetMaxVirtualAddress() support for LoongArch

Add support for getting the maximum virtual address, LoongArch has multiple
address space layouts, the default maximum virtual address of the current
user space is 47 bits. (from TASK_SIZE in the kernel for loongarch64).

Reviewed By: SixWeining

Differential Revision: https://reviews.llvm.org/D137219