Make GetPcAdjustment a free function.

We're now using it in contexts that don't have all of the registers available,
such as GWP-ASan and soon MTE, so it doesn't make sense to have it be a
member function of Regs.

Bug: 135772972
Change-Id: I18b104ea0adb78588d7e475d0624cefc701ba52c
diff --git a/libunwindstack/Unwinder.cpp b/libunwindstack/Unwinder.cpp
index 1bb0319..560030e 100644
--- a/libunwindstack/Unwinder.cpp
+++ b/libunwindstack/Unwinder.cpp
@@ -181,7 +181,7 @@
         step_pc = rel_pc;
       }
       if (adjust_pc) {
-        pc_adjustment = regs_->GetPcAdjustment(rel_pc, elf);
+        pc_adjustment = GetPcAdjustment(rel_pc, elf, arch);
       } else {
         pc_adjustment = 0;
       }