Set default CFA to stack register.

Set default CFA to stack register.

Without this patch the default is not set and will cause a crash in unwind handlers in libgcc when DWARF2 is used for unwinding.

ChangeLog:

  * config/tc-or1k.h:

  (tc_cfi_frame_initial_instructions) define.

  (or1k_cfi_frame_initial_instructions) prototype (body in tc-or1k.c)

  * config/tc-or1k.c:

  (or1k_cfi_frame_initial_instructions) set SP as the default CFA reg.