8283626: AArch64: Set relocInfo::offset_unit to 4

Reviewed-by: simonis, aph

Author: eastig

src/hotspot/cpu/aarch64/relocInfo_aarch64.hpp

@@ -29,8 +29,9 @@
   // machine-dependent parts of class relocInfo
  private:
   enum {
-    // Relocations are byte-aligned.
-    offset_unit        =  1,
+    // AArch64 instructions are always 4 bytes long and 4-aligned, so
+    // the two lowest offset bits can always be discarded.
+    offset_unit        =  4,
     // Must be at least 1 for RelocInfo::narrow_oop_in_const.
     format_width       =  1
   };