radv: add initial trap handler support with RADV_TRAP_HANDLER=1

radv: add initial trap handler support with RADV_TRAP_HANDLER=1

A trap handler is used to handle shader exceptions like memory
violations, divide by zero etc. The trap handler shader code will
help to identify the faulty shader/instruction and to report
more information for better debugging.

This has only been tested on GFX8, though it should work on GFX6-GFX7.
It seems we need a different implemenation for GFX9+.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6384>