drm/amdgpu: add support for IP discovery gc_info table v2

Used on gfx9 based systems. Fixes incorrect CU counts reported
in the kernel log.

Bug: drm/amd#1833


Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org