drm/amd/display: add non-DC drm_panic support

Add support for the drm_panic module, which displays a pretty user
friendly message on the screen when a Linux kernel panic occurs.

Adapt Lu Yao's code to use common helpers derived from
Jocelyn's patch.  This extends the non-DC code to enable
access to non-CPU accessible VRAM and adds support for
other DCE versions.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: Lu Yao <yaolu@kylinos.cn>
Cc: Jocelyn Falempe <jfalempe@redhat.com>
Cc: Harry Wentland <harry.wentland@amd.com>