drm/amdgpu: replace readq/writeq with atomic64 operations

[Guenter Roeck]

On Wed, Aug 07, 2019 at 10:56:40AM +0800, Tao Zhou wrote:
> readq/writeq are not supported on all architectures
> 
> Signed-off-by: Tao Zhou <tao.zhou1 at amd.com>
> Reviewed-by: Alex Deucher <alexander.deucher at amd.com>

Regarding the claim that this would work for 32-bit x86 builds:

make ARCH=i386 allmodconfig
make ARCH=i386 drivers/gpu/drm/amd/amdgpu/amdgpu_device.o

results in:

  ...
  CC [M]  drivers/gpu/drm/amd/amdgpu/amdgpu_device.o
drivers/gpu/drm/amd/amdgpu/amdgpu_device.c: In function ‘amdgpu_mm_rreg64’:
drivers/gpu/drm/amd/amdgpu/amdgpu_device.c:279:9: error: implicit declaration of function ‘readq’;

drivers/gpu/drm/amd/amdgpu/amdgpu_device.c: In function ‘amdgpu_mm_wreg64’:
drivers/gpu/drm/amd/amdgpu/amdgpu_device.c:298:3: error: implicit declaration of function ‘writeq’

This is with next-20190808.

Guenter