drm/amdgpu: cleanup amdgpu_bo_create()

Remove shadow bo related code as vm code is creating shadow bo
using proper API. Without shadow bo code, amdgpu_bo_create() is basically
a wrapper around amdgpu_bo_do_create(). So rename amdgpu_bo_do_create()
to amdgpu_bo_create().

Signed-off-by: Nirmoy Das <nirmoy.das@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>