Add support of frame unwinding for HS6x

[kolerov]

Right now frame unwinding without debug information does not work for HS6x targets. It happens because the prologue analyzer in arc64-tdep.c can parse 32-bit code only (e.g., HS5x code). For example, this code expects that all pushes and pops in a prologue store and load 32-bit value, but GCC generates 64-bit pushl_s and popl_s for 64-bit values (blink, fp, etc.).

I believe there are much more pitfalls regarding frame unwinding for HS6x code like parsing 64-bit stores and loads.

However, GDB can show a reasonable information about a frame using info frame when a program is compiled with debug information. In that case prologue analyzer is not used and all information is obtained from debug symbols.