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/LocalUnwinder.cpp b/libunwindstack/LocalUnwinder.cpp
index 5d81200..05650fb 100644
--- a/libunwindstack/LocalUnwinder.cpp
+++ b/libunwindstack/LocalUnwinder.cpp
@@ -106,7 +106,7 @@
     uint64_t step_pc = rel_pc;
     uint64_t pc_adjustment;
     if (adjust_pc) {
-      pc_adjustment = regs->GetPcAdjustment(rel_pc, elf);
+      pc_adjustment = GetPcAdjustment(rel_pc, elf, arch);
     } else {
       pc_adjustment = 0;
     }