drm/amdgpu: add UAPI to query GFX shadow sizes

Add UAPI to query the GFX shadow buffer requirements
for preemption on GFX11.  UMDs need to specify the shadow
areas for preemption.

v2: move into existing asic info query
    drop GDS as its use is determined by the UMD (Marek)
v3: Update comments to note that alignment is base
    virtual alignment (Alex)

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>