drm/amd: Remove inclusion of non-existing include directories

This patch fix the following build warnings:
  CC [M]  drivers/gpu/drm/amd/amdgpu/amdgpu_drv.o
cc1: warning: ../display/: No such file or directory [-Wmissing-include-dirs]
cc1: warning: ../display/include: No such file or directory [-Wmissing-include-dirs]
  CC [M]  drivers/gpu/drm/amd/amdgpu/amdgpu_device.o
cc1: warning: ../display/: No such file or directory [-Wmissing-include-dirs]
cc1: warning: ../display/include: No such file or directory [-Wmissing-include-dirs]
[...]
This warning is shown for each file in amdgpu directory, so it spams a lot.

Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>