drm/amdgpu: Move read of snoop register from guest to host

Guest is reading/writing to snoop register which is a security violation
We moved the code to the host driver
And also added a validation on the guest side to check if it's guest

Signed-off-by: Masha Grinman <Masha.Grinman@amd.com>
Reviewed-by: Harish Kasiviswanathan <Harish.Kasiviswanathan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>