drm/amdgpu: fix build error without CONFIG_HSA_AMD

If CONFIG_HSA_AMD is not set, build fails:

drivers/gpu/drm/amd/amdgpu/amdgpu_device.o: In function `amdgpu_device_ip_early_init':
drivers/gpu/drm/amd/amdgpu/amdgpu_device.c:1626: undefined reference to `sched_policy'

Use CONFIG_HSA_AMD to guard this.

Fixes: 1abb680ad371 ("drm/amdgpu: disable gfxoff while use no H/W scheduling policy")

Signed-off-by: Shirish S <shirish.s@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>