amdgcn: Support basic DWARF

amdgcn: Support basic DWARF

This is enough DWARF support for "-O0 -g" to work OK, within a single frame,
using the new rocgdb debugger from AMD.  Debugging with optimization enabled
also works when the values are located in SGPRs or memory.

Scalars in VGPRs are problematic, EXEC_HI and VCC_HI are unmappable, and
CFI remains unimplemented.

gcc/ChangeLog:

	* config/gcn/gcn-hsa.h (DBX_REGISTER_NUMBER): New macro.
	* config/gcn/gcn-protos.h (gcn_dwarf_register_number): New prototype.
	* config/gcn/gcn.c (gcn_expand_prologue): Add RTX_FRAME_RELATED_P
	and REG_FRAME_RELATED_EXPR to stack and frame pointer adjustments.
	(gcn_dwarf_register_number): New function.
	(gcn_dwarf_register_span): New function.
	(TARGET_DWARF_REGISTER_SPAN): New hook macro.