[amdgcn] Update CFI configuration

[amdgcn] Update CFI configuration

Currently we don't get any call frame information for the amdgcn target.
This patch makes necessary adjustments to generate CFI that can work with
ROCGDB (ROCm 3.8+).

gcc/

	* config/gcn/gcn.c (move_callee_saved_registers): Emit CFI notes for
	prologue register saves.
	(gcn_debug_unwind_info): Use UI_DWARF2.
	(gcn_dwarf_register_number): Map DWARF_LINK_REGISTER to DWARF PC.
	(gcn_dwarf_register_span): DWARF_LINK_REGISTER doesn't span.
	* config/gcn/gcn.h: (DWARF_FRAME_RETURN_COLUMN): New define.
	(DWARF_LINK_REGISTER): New define.
	(FIRST_PSEUDO_REGISTER): Increment.
	(FIXED_REGISTERS): Add entry for DWARF_LINK_REGISTER.
	(CALL_USED_REGISTERS): Likewise.
	(REGISTER_NAMES): Likewise.