Change the GetAdjustedRelPc to GetPcAdjustment.

This cleans up a bit of the Unwinder code to make it clear what's
going on.

Modify the offline unit tests to verify the pc and sp to make sure
that those values get computed correctly.

Test: Passes unit tests.
Test: Passes 137-cfi art tests.
Change-Id: I0787a1d77b8726d3defd08f31c7476f6798f8d0d
diff --git a/libunwindstack/RegsMips.cpp b/libunwindstack/RegsMips.cpp
index 6751f52..5d20bef 100644
--- a/libunwindstack/RegsMips.cpp
+++ b/libunwindstack/RegsMips.cpp
@@ -35,16 +35,12 @@
   return ARCH_MIPS;
 }
 
-uint64_t RegsMips::GetAdjustedPc(uint64_t rel_pc, Elf* elf) {
-  if (!elf->valid()) {
-    return rel_pc;
+uint64_t RegsMips::GetPcAdjustment(uint64_t rel_pc, Elf* elf) {
+  if (!elf->valid() || rel_pc < 8) {
+    return 0;
   }
-
-  // For now, just assuming no compact branches
-  if (rel_pc < 8) {
-    return rel_pc;
-  }
-  return rel_pc - 8;
+  // For now, just assume no compact branches
+  return 8;
 }
 
 void RegsMips::SetFromRaw() {