drm/amdkfd: Move gfx12 trap handler to separate file

[ Upstream commit 62498e79 ]

gfx12 derivatives will have substantially different trap handler
implementations from gfx10/gfx11. Add a separate source file for
gfx12+ and remove unneeded conditional code.

No functional change.

v2: Revert copyright date to 2018, minor comment fixes

Signed-off-by: Jay Cornwall <jay.cornwall@amd.com>
Reviewed-by: Lancelot Six <lancelot.six@amd.com>
Cc: Jonathan Kim <jonathan.kim@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Stable-dep-of: d584198a ("drm/amdkfd: Ensure consistent barrier state saved in gfx12 trap handler")
Signed-off-by: Sasha Levin <sashal@kernel.org>