drm/amd/amdgpu: Add gca config debug entry (v4)

A binary entry that lists GCA configuration data (and can be
read by umr).

(v2) Use kmalloc instead of vmalloc
(v3) Minor indentation correction
(v4) agd: Squash in kmalloc fix

Signed-off-by: Tom St Denis <tom.stdenis@amd.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>